What is the procedure to downgrade an Ami BIOS with fpt?


I have been searching the internet now for 2 days and still don’t have a clear idea how to downgrade my bios.
I bought a second hand HP Spectre X360 15-ch075nr. It is working great except the right speaker has low crackling sound and I understand this is a bios problem.
Now I don’t want to upgrade my bios because of all the intel microcode patches that come with it, it seems they are now even locking down cpu undervolting.
So I want to try downgrading the bios but that is also locked by hp.
I read that it might be possible with fpt, but on this form I saw a warning not to us the standard 083ba.bin file that comes with the hp bios packages because it deletes the UUID, Serial, DTS Key?
I also see that the dump made by fpt is smaller (6mb) then the 083ba.bin file (8mb).
So what do I do?

It seems FPT and AFU don’t work since it is locked, als the HP BIOS Configuration Utility (BCU) doesn’t allow to unlock it.
Does anyone know how to downgrade the bios (without unsoldering and hardware programing the chip) or is it simply impossibe on a hp spectre?