Seems like you've embedded code in OptROM that you copy to ALT-LCD. When you say "the cold start recovery routine of TS-DOS" do you mean the NEC POKE and EXEC to activate TS-DOS?
If so it seems your only trigger to do the LINE install is the BASIC ROM's OptROM install EXEC routine. So whenever the ROM installs, it will fill in your code into ALT-LCD. I can't think of anything that you would have to do different than whatever TS-DOS does. I suspect some stack imbalance, clobbered registers or clobbered RAM variables. -- John.
