You can swap the shark fin for the factory puck antenna. You'll retain SXM/GPS but loose cellular. You may want to consider a posting in the wanted section of the forum. Many remove their puck to add the sharkfin and may have one laying around they would sell. Possibly might find someone wanting to trade too.
Yep you can replace it at the radio with something like this for GPS only, but I don't think it's large enough to plug the hole in the roof if he removes the sharkfin.
Bingfu Vehicle Waterproof Active GPS Navigation Antenna Fakra C Blue GPS Antenna Compatible with Ford Dodge RAM GM Chevy Chevrolet GMC Jeep Cadillac BMW Audi Mercedes Benz Car Truck SUV Head Unit
https://a.co/d/gSfcX4P