What are the circumstances where autovacuum can be disabled?
(to prevent wraparound) 


is the key bit. PostgreSQL must do freeze vacuums where transaction IDs are set to XID_FROZEN to prevent transaction ID wrap-around, and as a result massive data corruption.

If you disable these or cancel them all the time your database will eventually go into emergency shutdown.

See the user manual on VACUUM.

You can do a manual VACUUM FREEZE during a quiet period to get this all over and done with in one go if you want.