For AMD(ATI)
Take the program Phoenix Tool, unpack the bios file.(for example Quanta LX8)
Take the TotalCommander or alternative.
Search in all files of unpacked bios HEX value ID of you chip.
For example, change 216-0752001 => 216-0752003
ID original chip is 0210 1297 in HEX, Start the search in the directory "dump"(TC or XSearch)
We will find several files, includes this signature
54147C6C-5C82-4518-8232-6D54536CD88E_0_329.ROM
28646679-B110-4DE0-A1F8-6B3C4CD282E1_0_331.ROM
981A25E0-0D83-436D-9184-C1AA53BB143A_0_105.ROM
C95E6A28-FB95-49F2-AE01-F38166FD4524_0_29.ROM
PADDING-00186048_0_380.ROM
Find in web, ID of 216-0752003 is 0210 1397.
Change all hex value 0210 1297 to 0210 1397 in HexEditor, save changes.
And assembling the bios file back by PhoenixTool.
Example by Chernomor
download/file.php?id=39287ID of some chips by Genadiy58
download/file.php?id=39533download/file.php?id=39611More info
viewtopic.php?f=181&t=19804 Some chips ID of IGP
215-0752003 0x9714
215-0752016 0x9715
215-0752001 0x9710
216-0752001 0x9712
216-0752003 0x9713
215-0674028 0x9610
216-0674026 0x9612
216-0674024 0x9613
215-0674042 0x9616
215-0674032 0x9614
215-0674058 0x9616
Important! in hex change bytes: 0x9714 = 1497 (big-endian)