Subject Cannot transliterate character between character sets for Firebird 2.1 database with WIN1257

I am trying to migrate Firebird 1.5 dialect 1 charset NONE database to Firebird 2.1 dialect 1 charset WIN1257 database, that still will be used by BDE.

All is working. The only problem is that metadata (code of procedures or triggers) can not contain WIN1257 specific characters (with special marks). Such procedures compile and and can be executed but when they are viewed with IBExpert of Flamerobin, the exception 'Cannot transliterate character between character sets' is raised.

We can avoid use of WIN1257 characters in metadata, it is sufficient that they are used in data (even BLOB fields handle them OK), but can this raise issues later (which is hard to predict now from our experience only)? What is the best and fastest path to make such migration?