The previous rationale for not allowing manga titles to update (at all) was that it would be confusing for users if a manga's title arbitrarily changed when the source changed it. Presumably, users would care less about this arbitrary change for manga that is not in library, so this provides a path for getting a manga's title updated, and prevents incorrect titles from persisting in the DB for manga that get title updates but aren't in library.
(cherry picked from commit 58a871c8cc600dbf59691e9c51413ef9b7da3796)
23fae05694