Okay, this went less well than expected
When I removed the masks, the ones for the stars and the 7s were stuck much more strongly than I thought they would be, and so I had to peel and scratch them off with a knife — with the results shown above.
In retrospect, the cause is obvious. I had used PVA(-like) woodworking glue to stick them on, but hadn’t bothered to check the exact type. Turns out this particular bottle is intended for in- and outdoor use, and extra strong, which apparently makes it stick to paint
much better than I thought it would. I’ve never had this happen in the past when I used straight PVA glue, with which the masks just peel off the model and leave nothing behind. The obvious lesson is to pay more attention to the glue next time
Nothing to do but fix it with a brush: