This is what I do when a rim wears out due to brake-track wear. I loosely tape the new rim alongside the old wheel, loosen the spokes, and then move them over to the new rim one at a time. Keeps all the spokes in the same position on the hub so they still lie in the same groove they may have created in the hub flange and should minimize any stress. If you know the current rim model you can look up the ERD on one of the wheel-build programs like Spocalc and then see what other rims have close to the same ERD (also check where the spokes on the current wheel bottom out in the nipples so you know if you can go bigger or smaller on the new ERD).