[@DarkwolfX37][@Flamelord][@Ariamis] 
[quote]"Or maybe you're the self-sacrificing sort - hoping to keep the coin out of the hands of those who are less principled than yourself."[/quote]
I'm just thinking, you wouldn't need to keep the coin out of other people's hands if it couldn't be taken from you. 

[quote]"They’ve got dirt on and favors owed from YOU, and as a ruthless shadow cabal, they’ll use you. Their goals are unclear and mysterious, but at the very least, they’ll have you informing on your other Patron if you have one. They don’t ask for much at first, but they will ask you to do things just out of your reach, enough that you’ll need help, or resources you don’t have. And when they give them to you, you’ll still be in debt. The longer you work for them, the more unsettling the things they ask you to do become."[/quote] 
The description on the drawbacks imply that the Mint has more than just one thing over their magical girls. The plural is used several times and it is what they use to coerce the behavior they want. Otherwise they wouldn't select that person because they would have no influence over them. You get one black coin so they must have something else on you or you're no use to the Mint. Also the Mint will do things to put you in a poor position so you will need their help some way or another and further build debt. I doubt the Mint, given their power and influence, would allow such a simple loophole break their system. They play by their own rules and bend them as necessary. We're not talking about the Beacon here. I suppose if a magical girl has lost their usefulness to them they could alway let it go.