If I would get access to the key?
Quite easy to answer for me, because I thought about this a hundred times!
Case 1: Short, but unobserved access to the key:
I would just open the main lock and put the key back to where I found it. Then I would probably look for some privacy, take the belt off and take on long and covering clothes. I would take it back on in the evening, before my mom could recognize it. In the meantime, I would enjoy to take the opportunity to go out of the house FREE. I didn't do that since almost 3 years (except 3-4 doctor visits while closely accompanied by my mom)! And I would make sure to not get back into my belt unrelieved 😉.
Possibly, I would even try to find a replacement lock of the same type and use this until my frequent unlocking day. That would be even better! Depending of the point of time, this could mean to be able to let me out by myself for up to 2 weeks!
Case 2: Assured unobserved access to the key for at least a couple of hours:
I would go to a shop and make a copy of the key. This would allow me free access to my belt until my mom replaces the lock, which happens sporadic every few weeks to some months! Clearly my favorite case!
However, possibly it would be very hard for me, when I suddenly see my mom putting a new lock in place after some weeks or month of occasional personal freedom!