I know they're length of stay but if I move resort can I still use them in the next resort?
Really? Wow. I didn't realize that, either. I thought it would be for your entire vacation. Huh.
Well, that rather sends a subtle message then. If WDW wanted to truly restrict them to a specific resort, they'd make it happen. If the mugs are generic, that pretty much says, use them at whichever resort you happen to be. I'm not up on my "mug rules and restrictions though" as we don't drink soda, so don't buy the mugs.