I was going to suggest to Diden yesterday, that he get changed behind some secluded thick shrubs, a high fence or a garage (somewhere near the school).
But I was worried there would be a possibility that he might accidentally get noticed by someone. >.>
So yes, your suggestion Sacrament, of a nearby coffee shop etc that has a bathroom, is an infinitely better place to change clothes, before getting to the school. :thumbup:
If she absolutely will not allow you to go out with season-appropriate clothing, ask her to get you some long johns to wear underneath your clothing. They keep you warm and aren't bulky. These, plus a regular winter jacket should be more than enough protection for mildly cold weather. You can change out of them at school if you feel like it.