You can set new BIOS aside and not write to it if you want. Did you already test and confirm it's working? If not, do that before anything else, so you know it's working BIOS.
Hot swap can be risky yes, but as long as you prepare in advanced it's usually OK. Practice removing and inserting chip halfway with no power on the board, that way you are used to moves you will make with your hands.
You can put tape or string, something around each chip too, from the bottom around and out both sides, then either coming together on top or leave off to the sides. Made it wide so it's not tiny/thin string, like half a party ribbon or some strip of plastic from a baggie top or something.
Pull straight up to remove, and then carefully set into place when putting back, you only have to push about halfway down, so you can feel it's making firm contact and well aligned as you push down lightly.

Yes, if you don't want to hot swap a flash programmer will be much easier to use.

You can flash the BIOS you have without all that though, you just need to find USB that will work with flashback on your board, smaller is often better (512MB-2GB)
I can send you AFU versions that /GAN does work on, and a special Asus version of AFU too. But those will only help if you have a running board, then you'd need to do the hotswap in DOS to flash the other chip.
If you have one working chip now, then nothing to worry about, use that for now and order the $3 flash programmer and then once it arrives weeks from now you can reprogram your other BIOS to keep as backup.

Hi,

I guess I was not 100% clear, yes the new chip is working, it's in my PC. I ordered it via Ebay and have again the official 2501 of Asus inside for the M5A99X EVO R2.0
The other chip is outside, I failed to program a new version in it, so PC was dead (came up with Bios is in recovery mode).

About flashback:
Actually I tried 4 different USB sticks, 3 were maybe with too high capacity, but one is 2 GB only. I tried both Fat and Fat32.
What I have seen is: The stick is not accessed at all! No lights come up on the stick. So my assumption was that the flashback does not work.

I tried hard to do it, because after killing my BIOS with afudos, I though I still can do it with flashback, but :-(
Unfortunately I don't have 512MB stick....

There are 3$ flash programmers???

FAT32 is what you need to use, maybe 2GB was incompatible like the larger ones, you'll have to try more smaller USB Sticks until you find one that works.
Usually when USB stick is not compatible it will often light up still, but either only a quick flash or a solid LED, not blinking for 1-2 minutes like it would during normal proper operations.
I am not sure about the flashback button LED itself with incompatible USB, not sure what it does I mean, I'm only referring to the LED on USB Sticks with LED. USB Flashback button must be pressed in and held for 3-5 seconds to start it.
Your board page says "Any USB Port" which may be OK, but I would mainly use the black 2.0 ones under LAN, or a red one, so it's USB 2.0. I've never seen this work on USB3 ports, but it may, I'd avoid using those and go with the black under LAN>

Yes, $2.50-3 programmers all over ebay, search CH341A flash programmer

If you want to get that other chip programmed now, without programmer, you'll have to do hot-swap. Either boot to DOS with flash tool and BIOS ready on USB, then pull working chip out and place in old one, then reflash.
Or boot to BIOS with BIOS on USB ready, get all the way to EZ Flash page, remove the good BIOS and put on the old one, choose your BIOS file and flash.
If you can get backup via FPT or AFU, or Asus tools (AI Suite or EZ Flash backup) use that instead of stock BIOS to flash either of these ways, that way your serial, UUID, LAN MAC ID etc will be in the BIOS.

Hello again,
OK, I will try tomorrow again:
First I try again ASUS flashback, with the bad BIOS chip (the content, the chip itsself should not be bad).
But most likely I will fail, because I tried already very often.

So I have the possibilty to make a hotflash to the bad chip or to normally flash my working BIOS chip.
But what method do you recommend for me?
"Boot to BIOS and go to EZ Flash Page" won't work with the cap file, right? Same for Boot with a DOS CD with afudos on it (I have such a CD ready, that's how I destroyed my BIOS), also does not work with a cap file.
So I convert the cap file to binary? And then use what?

I attach the modified bios, should be right, I only added the NVMe module. Can you check that, too?

Thx in advance for your answers.

Addendum:

Just tried out: Asus EZ-flash does not allow (of course) to program my modified cap BIOS => security failure.

For modified BIOS you have to flash a certain way, using AFU or AI Suite, or USB Flashback - [Guide] How to flash a modded AMI UEFI BIOS
For the mod BIOS, in this instance and for quick and easy way, I would flash the stock BIOS in there first, then flash again using AFU and /P switch only, that is all you need from the mod BIOS.

AFU works with cap file, not modified one, use /CAPSULE Switch. If you want to remove the capsule for easier flashing, open in UEFITool and right click the first section shown in the middle (AMI Aptio Capsule) and choose extract body, this is your BIOS rom 2KB smaller than the cap file.

Or, since this is backup spare BIOS, just flash stock BIOS into the chip using EZ Flash, you'd be done by now . And yes, EZ Flash works fine with .cap BIOS, just not modified one in many instances.

Your NVME insert is OK!

Hi, thx again for the quick answer.
Please don't link to this guide, it's not helpful for the case that flashback is not working.

So if I understand you correct, I shall:
1) start with the original BIOS
2) Convert my cap file according to your description (This part is missing the guide!!!!)
3) program the bin file with afudos and parameter /P only.

Typo corrected

Correct?

Flashback works, you just need to find compatible USB stick. AFU works as well, as does AI Suite method.

Yes, but use /p switch not /b

ARRRRRGHHH

OK, I managed to make a hotflash of the destroyed Bios chip, so I now have to working chips with ASUS original Bios 2501, fine.
I can't do flashback, all my sticks are not compatible as it seems.

Good, I created a file "bios.rom" with UEFITool following your description, and yes its file size is 2 kByte less.
Good, I made a bootable USB stick with FreeDos, put afudos.exe and bios.rom it the start:
afudos bios.rom /P

I get something like (I wrote it on paper, obviously I could not use cut and paste)
AMI Firmware Update Utility v3.07.1
Reading flash ... done
FFS checksums ... ok
1e - Error: Secure function is not supported on this file.

How can I program my bloody modified Bios?

OK, I made more tries:
Here in the forum an older version of afudos is linked, which support /GAN
I made several tries, and finally I did not get ANY error messages, when I used:
afudos bios.rom /GAN.
Horray, I programmed the mod. bios, or not?

I do not see any difference now, I hoped I have a possibilty to choose the SSD as boot device.
It does not show up. What would be the expected behaviour?
How can I check the I really programmed the new BIOS?

The NVM SSD (Intel 600p) is fully usable under Windows 10, but that worked before, too ...

Great job!! One day you will find USB Stick that works with your USB Flashback!

Yes, when you used /GAN it flashed, I assume, no errors correct and it showed "Updating Progress" (reading, erasing, flashing) correct? To verify if your mod BIOS is on the board BIOS, make a dump from the chip, then open that file in UEFITool and see if your mod change is there or not.

To make bootable NVME you have to follow the guides on how to set that up, usually you cannot see it how you would expect to be seeing it look in the BIOS (I think it shows as PATA or something odd/unexpected). Check the guides on that, it's all explained.
If you could always see NVME in windows with this motherboard, BIOS mod is not required at all, and should not be done since BIOS is already made NVME compatible from the manufacturer.

Hi again, unfortunately it was all in vain:
afudos with /GAN writes out erasing .... programming ALL, no error messages, but then nothing is programmed.
I rebooted, started again afudos, save bios with option /O. Then I rebooted again to Windows and compared my modified file with the save file, the NVM module was missing.
I could not believe it, programmed the BIOS 3 times, NOTHING.

So now it's clear why I did not see any change in the BIOS, there was none.

I have read now all the postings in the thread, and it confirms my finding: when you have a security protected Bios, you can't program it with Afudos, it simply does not work.

I also tried the AI-Suite trick, it's actually very simple: Before starting the real upgrade, you replace the original Asus Bios with your modified Bios. And it starts programming.
After 2 minutes it was finihed and it suggested a re-boot, I did, booted to FreeDos, saved bios, booted to Windows, checked the save Bios with UEFITool => NVMe module missing again :-((((
So same behaviour as with afudos /GAN, it takes some time, pretends to do something, but no change to the Bios.

Now I understand why CodeRush wrote : Afudos does not work, get a programmer.

Try next version that supports /GAN - I sent you PM correct with several DOS and a windows version? If it was Intel I could help you flash with FPT, but yes if you cannot get it with AFU you will need programmer.
And, aside from all these reasons, everyone/anyone looking at any Mod BIOS should pickup programmer first just in case, they are only $3 or $6-7 if you need cable too.

Did the package I sent you contain wAsusFU? If not, I will send, not sure if it will work on your board but we can try.

Hi,
You did not send me anything.
I used the latest AFU (downloaded from AMI) which included Windows, DOS, ..... afudos was version V3.07.01. *** EDIT That version has no /GAN support ***

For my tries with /GAN, I used afudos.exe (downloaded here from this thread) it is version V3.06.01.

The mainboard is Asus M5A99X EVO R2.0 it is an AMD AM3+ board, with AMD chipset.
Please send me something, that works ;-)

Sorry, I thought I sent to you! PM Sent