That would be so good. Maybe a level based unlock system. Like at level 10 you get your entrance text unlocked, at level 20 your victory text and so on. All my glads start around level 10 to show their "character" and about level 30 you see the potential natural kill ratio of that glad, so a kill text unlock at level 30 would be appropriate.

With that system the customized text would come naturally and would solve the problem with new managers glads abusing the custom option. but a on/off for each stable is a safer way.

An other idea would be Nate gives us text pieces which provides a divers customization without the need of blocking someone for bad "taste".