And can we know the specs of the HP original sticks and the new ones added…
EDIT: No faith on success but ill point you some directions…
You can try IFRextractor and look for any related info, a little guidance here
The system board seems to have an FDO jumper (Flash Descriptor Override), this will usually allow the Intel FPT tool to access SPI bios regions (Your Intel ME FW version based… v16?) for read/write operations and from there dump only the bios_region and work from there, mod can be flashed then with same tool, usually.
Notes… due to what you already know from flashing mods on HP branded systems and other OEMs, you have a very high chance of killing the system, so if you don’t have experience working with these tools and don’t know how to recover a death system, i do advise you NOT to proceed.