Thought it would work because you can use it to get foreign Pokemon events but I guess not, i don't have a non US 3ds or know anyone who has one to test it out
1. if you still have your HS.app you can Injeted it back into your NAND with decrypt9 but if you don't have it i Don't know of a way to get it back I know there is A way just don't know what it is
2. you can use luma locale switcher to run a game as a different region to play cross-region Local...