Hi Susan,
First, why not to replace old PT by new PT in custom code? Seems fairly easy. Find all places where it’s in use with some search tool like program RS_ABAP_SOURCE_SCAN. Replace where needed.
Second, if you absolutely want to stick with old PT then be ready to deal with side-effects i.e. open items containing old PT (you might want to change baseline date massively) and calculations such us Net due date in FBLxN not working properly anymore for some items or accounts. Not sure how APP and standard evaluations might react as well.
Best regards,
Anton
