Hello!
If you have datasheet for the chip you want to support, you can follow the guidelines: https://flashrom.org/contrib_howtos/how_to_add_new_chip.html
But this would also need you to have a dev environment (not the machine with broken motherboard) and, an external programmer, is this something that you have?
How does the process work when recognizing chips ? Would adding this chip create a conflict with its predecessor ?
If there are multiple chips with the same model ID, flashrom will tell you that after probing, and will tell you to pick which one you have and re-run. There is also details on manpage https://flashrom.org/classic_cli_manpage.html#options