I wish this "lock" didn't exist or had a toggle.
From full maturity I once put on a diaper, had an "accident", changed into another one, had another "accident" and suddenly I could no longer change my own diaper.
I get what it's going for, but honestly it's kind of frustrating that it's punishing you for engaging with a mechanic of the game because you can't choose what diaper to change into afterwards, which isn't really fun when there are so many different brands in the game. And from what I'm aware of there aren't actually a lot of places to get someone to change you to begin with.