"add (mathematically) together all original hex numbers what you intend to modify in the BIOS"
That would be:
11 0E E5 00 E6 00 (the original vendor and subsys IDs, omitting the F7)
"and also add together all hex numbers what you write in!"
4F 14 84 70 88 70
"Then subtract from the original sum the new sum. "
So 1EA (original)-24F (new) = FFFFFFFFFFFFFF9B
"If there is a positive number then somewhere at the end of the bios file find a 0 (where seems no live code or data) and modifiy (add) with the result. If there is a negative number then find a FF ( at the end and ..) and also add ( effectively subtract ) and modify with. "
Well it's obviously a negative value - this is where I'm now confused. What do I do from here?
I've never meddled in this stuff before so would appreciate a little help