Using GPE for an action that standard script uses a gosub

Hey, I need to make a modification to a script called SUBSMXA. The standard script is SUBSMX, and it is linking the SUBSMXA via gosub. 

What I am trying to do is make a modification (adding something, not removing anything) to one of the actions in the SUBSMXA, but I would need to do that in the Specific script so it doesn't get erased by a patch. The specific script is called SPESMX. So if I write the following code:

#########################################

$LIENS

GPE=1

BLAH BLAH BLAH MY CODE

RETURN 

#########################################

Would the SUBSMXA script know not to read the $LIENS action again?