Hey guys i got a question that might sound stupid idk.
Would it be possible to edit a bios to use the cpu microcode from an older version?

@haxzion - Yes, easily possible and people do it all the time!
[GUIDE] Update CPU Microcode + Fix FIT Using UEFITool / Hex

Wow thanks, i got some reading to do....Do you think this guide will work with my z370 board?

Yes @haxzion - I update microcodes all the time in all boards, and that method directly applies to your boards BIOS. Although, I didn't make the microcode update part very detailed in that, sorry about this, that guide was mainly for correcting _FIT_ Table which you need to do after microcode updating.
Here is another microcode update guide too, it's linked in that guide - [GUIDE] AMI INTEL CPU Microcode Update Guide

You can also simply use UBU tool to update your microcodes if you wanted - [Tool Guide+News] "UEFI BIOS Updater" (UBU)

Thanks a lot....I will start reading tomorrow :)

I finally did it....I used UEFI Bios Updater (UBU) in order to use an older microcode but with a newer bios,since i wanted to avoid all the meldown/spectre fixes and thier drawbacks.
I also followed Lost_N_Bios guide on how to make the modded gigabyte bios flashable and it worked perfectly.

After i flashed the modded bios i noticed that windows was still using a newer MC. At first i thought it had something to do with the backup bios but after some thinking i realized it was Windows 10 v1809 microcode updates.So even if you are running an older bios/MC Microsoft is pushing the updated microcodes though the OS.
In order to fix that i took ownership and then replaced the file C:\Windows\System32\mcupdate_GenuineIntel.dll (for Intel CPU) with an older one (pre meltdown/spectre)
and VOILA Windows picks the microcode from my modded bios.No more meltdown/spectre crap.Let me know if you want me to post any files.

Thanks a lot for the help :)

Glad you were able to figure all this out yourself @haxzion good work