If you're less than 20, with a big bucket of luck, it can happen. The bones, I mean. But I mean it. A big bucket of luck.
Past that, any shrinkage is muscle only. See on the outside side of your feet. There's a soft area, right ? Past the small toe. That can shrink, which would make your feet more slender, thus fitting thinner shoes. If the LENGTH reduces, you've either gotten used to smaller shoes, have found a bigger-sized brand or have been bestowed a miracle. Or maybe the soft part of the heel can shrink, minorly reducing the length, but... Well, in any case, you should not expect it. If it happens, take it like a happy surprise.