IDA Pro or Ghidra, decompile and do what you want

Hm. Can't be a few NOP instructions be added simply?

First step is to get the BIOS up and running in an emulator so you can test your changes.
For changing strings, you can use a hex editor. You can only do in-place replacements of existing characters though--you can't lengthen or shorten the string.
However, if you make any changes to the BIOS, you must either update the checksum or locate the checksumming code and disable it.

jakethompson1 wrote on 2023-06-25, 02:50:

However, if you make any changes to the BIOS, you must either update the checksum or locate the checksumming code and disable it.

ROM BIOS piracy was a big thing in the Turbo XT era. Some far-east clones shipped with BIOSes that were taken from original vendors. To combat ROM privacy, many BIOSes of that era contain extra checking code (sometimes even multiple copies of it at different location) making sure the copyright strings are not modified, and otherwise crash the system during boot.

Robin4 wrote on 2023-06-24, 16:22:

Second problem is on the second screen says `Submarine Personal Computer XT` I want to change Submarine in XPC

And this change might trigger the ROM piracy protection, so be prepared for some extra work.