When the mod is installed, it will clear out any currently set custom titles so that limits so that the users have to re-add them and follow the enforced limit
When the mod in installed, don't reset any currently set custom titles. This technically means there could be custom titles longer than the requested limit set by the mod; however, if they try to edit their title after it would have to follow the enforced limit.
This is untested on 2.1.x but it may work if the structure hasn't changed.