Why do you want to turn off autonumbering for change objects? Maybe because change numbers are generated in ERP?
People are passionate about this for product data (Parts, Documents, CAD Documents) and we ended up making those manual number (after lots of intense debate) but have left all other object types auto number.
Note - What helps a lot is to use prefixes and / or suffixes for the auto-numbered change objects - which is done in OIR's. We also manually enter an ERP tracking number in the Windchill change using a custom attribute.
example
[cid:image001.png@01CF8557.BEC76020]
[cid:image002.png@01CF8557.BEC76020]
Note - if you use autonumber, make sure to change the related database sequence to no cache - else you skip up to 20 numbers every time the database is restarted. It's incredible that the Windchill installation does not set all sequences to NOCACHE.
[cid:image003.png@01CF8557.ECEE6890]