He may have said that. But to "change my address" when I've moved I have: rented an apartment, connected utilities, got a job (unless I moved because I already had a job in the new area), got a new driver's license if needed or changed my address on my old DL if still in the same state, registered to vote or changed my address on existing registration, and insured my car with new company if required, changed registration/bought new plates, etc.
So far as we know, neither GP nor BL did any of those things in NY. I think they were just visiting for GP's brother's high school graduation. They may not have intended to return to live with the Laundries but I don't think they were NY residents either.
JMO