This is indeed what server extensions where not designed to be. You will have a hard time coding around this, so better leave your hands off that schema changes.
How about having the schema mapped to a SXS all the time, and another document inside the DB acts as configuration parameters for the SXS? Then you could tell your SXS there what to do when, and the SXS might store the documents via callbacks in Tamino once, and somewhere else in other times…
Hiran
#webMethods#Tamino#API-Management