I doubted I would be able to. Nothing like proving yourself wrong.
Managed to take the disassembled ROM code. Remove the offending BREAK routine and Border flicker.
Plato works perfectly.
So, I have not only had some C code published. I have now written a library/driver, with some assembly in it. Probably to be cleaned up and accepted by a compiler maintainer.
Still can't believe the silly buggers put a check on the break key in there, and a half check at that!!!
Me, slightly crazy engineer type. Generalist in nature, hardware or software with nonspecialist skill set.