I have been playing with Coffeelake for over weeks to mod custom bios for MSI z170a gaming m5 with i5 9400F. But only one thing I can't figure is the "MSI warning", which is ' This MSI motherboard can't work with coffee CPUs rev. U0/P0 without changing BIOS region from compatible Z370 donor if it exists.' Because my board kept black screened after being flashed by a CH341a programmer. So, I assume that the Z370 donor would be the key solution I need to ask.
Did any experienced users in here figure how to dump or mod the custom bios correctly for MSI z170 board? If anyone gives me some hints or the right solution, I would really appreciate it.
Please let me know.
Thanks.

EDIT by Fernando: Thread title shortened

Z170A GAMING M5 support
latest bios version is 7977v1I (2018-07-02)
i have updated modules and microcodes,also added an extra microcode (i5-9400F=906EA) here.thats a start,you need to check relevant threads for more information

Notice: can be used by every z170a gaming m5 owner

how to upgrade/downgrade Management Engine:
Intel (Converged Security) Management Engine: Drivers, Firmware and Tools

How to flash a modded AMI UEFI BIOS
Coffee Lake CPUs on Skylake and Kaby Lake motherboards
and more..

As rule of thumb,keep your OS,apps,bios and drivers updated

I just checked your reply.
I really appreciate your time for my trouble, I really do.

I will carefully read and follow this guide.
Again, thank you for your help.

P.S If I bump into some issues, I would ask you one more time :D

@adayafterdeadline Also keep in mind that the 9400F has 3 potential steppings, U0, P0 and R0.

To ensure you are using the correct microcode you can check the S-spec on the box or CPU h̶e̶a̶t̶s̶i̶n̶k̶ [edit] heatspreader i.e.

CPUID 906EA = S-spec SRF6M = U0 stepping
CPUID 906EB = S-spec SRFAH = P0 stepping
CPUID 906ED = S-spec SRG0Z = R0 stepping

custom Z170A GAMING M5 with 906e9,906ea,906eb,906ec,906ed

Notice: cant be used by regular z170a gaming m5 owner

@onuracengiz That BIOS will not support Coffee Lake (or any CPU), you need to do more than just swap microcode for Coffee Lake to work in a Z170 motherboard, you must also downgrade the ME FW to version 11.7.0.1xxx or 11.6.x.

The BIOS also needs to be patched in several other ways to support Coffee Lake and the MSI Z170 Gaming 5 is particularly troublesome and requires the BIOS region to be ported (swapped) from the MSI Z370 Gaming 5 to use 6 or 8 core Coffee Lake CPU's, and even then there will likely be issues such as USB 3.x ports not working (ASMedia ASM1142 vs ASMedia ASM3142), onboard audio not working (Realtek ALC1150 vs Realtek ALC1220) and ethernet not working (Killer E2400 vs Killer E2500).

@adayafterdeadline For that motherboard I would only recommend B0 stepping CPU's which limits you to quadcore Coffee Lake CPU's such as the 8350K, or 8100 (also 9100F or 9350KF if you can find the B0 stepping, I've never seen one).

You could use CoffeeTime 0.92 to attempt modifying the latest BIOS 7B58v1A as you have a programmer to recover if it does not work (assuming you made a backup of the original BIOS).

Thanks to all of you.

Once I do this job this weekend, I will update the progress here.

I'm modding the Z370 bios as you suggested. I did downgrade ME to 11.7.0.1229 with enabled, but for VBIOS+GOP, I wasn't able to downgrade them any lower from 1063 and 9.0.1086 because of not matching the table size to several sections.
Do you think this could be the matter? As long as I can post the bios into the Z170 motherboard I have with the Z370 bios, I can definitely give up USB 3.0, onboard audio, and ethernet.

@adayafterdeadline The latest BIOS for the MSI Z370 Gaming 5 (7B58v1A) has VBIOS 1063 VBT version 2.09, which is compatible with Skylake, Kabylake and Coffee Lake.

It also has GOP 9.0.1086 VBT version 221 which is also compatible with Skylake, Kabylake and Coffee Lake so no change should be required - good luck!

Late update,

I tried every suggested comment above, however, they all failed on me, OMG.
I'm literary giving up on this motherboard and will look for another board sooner or later.

Thanks to everyone who suggested it here for me.