I have a Pokemon Scarlet joycon that stopped working after I opened it up for a repair. I double/triple checked everything and it’s all connected, I let it charge and nothing. I don’t really want to send it to Nintendo since they don’t guarantee a replacement of the same style. Should I take it in somewhere to be looked at, or should I just buy a replacement and do a shell swap?
No. Opening a device is categorically NOT a warranty voiding action, by law. At least in the US. Though, in this case, it does sound like they damaged the joycon, which would make it not eligible for warranty, but it has nothing to do with opening the device.