I have tested this, and ChangeAIScript("...",OVERRIDE) for Player1 persists across savegame, area transitions, and chapter transitions. I have yet to check what happens at shift from SoA to ToB, but I believe that will also work. It is probably due to Player1 not having a pdialog.2da entry to be reset to. The OVERRIDE script behaves as usual whether party AI is on or off, which was the problem with trying to use the default script. I am planning to use this instead of appending scripts to baldur.bcs and baldur25.bcs, which I have seen warnings against doing.

Now, this is really a resource that should be shared with all modders, which means adherence to some standard protocol. What I propose is Player1.bcs for SoA and Player1T.bcs for ToB. To that end, I have introduced the scripts in:

1) AR0602.baf -

IF
G("RjaliGen",0)
THEN
RESPONSE #100
ActionOverride(Player1,ChangeAIScript("Player1",OVERRIDE))
SetGlobal("RjaliGen","GLOBAL",1)
Continue()
END

2) AR4000.baf -

IF
G("RjaliGenToB",0)
THEN
RESPONSE #100
ActionOverride(Player1,ChangeAIScript("Player1T",OVERRIDE))
SetGlobal("RjaliGenTob","GLOBAL",1)
Continue()
END

In setting up the scripts themselves, I have used the following WeiDU code to avoid conflict with prior usage:

// Establish Player1.bcs and Player1T.bcs

ACTION_IF FILE_EXISTS_IN_GAME ~Player1.bcs~ THEN BEGIN
EXTEND_TOP ~Player1.bcs~ ~Rjali/Scripts/SOA/Player1.baf~
END
ELSE BEGIN
COMPILE ~Rjali/Scripts/SOA/Player1.baf~ // Create Player1.bcs
END

ACTION_IF FILE_EXISTS_IN_GAME ~Player1T.bcs~ THEN BEGIN
EXTEND_TOP ~Player1T.bcs~ ~Rjali/Scripts/TOB/Player1T.baf~
END
ELSE BEGIN
COMPILE ~Rjali/Scripts/TOB/Player1T.baf~ // Create Player1T.bcs
END

Some consensus should be reached for naming of the GLOBAL triggers, but I am hanging out here all on my own for the moment.