PRN = Pseudorandom Noise code. This is the spreading code or cypher key for the satellite you are listening to. It allows the rake receiver to extract the GPS signal from a wideband noise signal. More.

The antenna simply unplugs and gets replaced. It may be in the shark fin making things more expensive. The connector could be FAKRA or MCX or MMCX. Take some pictures of the back of the unit. If it is in the shark fin, consider relocating the antenna to the position used in the retrofit. In the E46 this is in the parcel shelf, but you won't have a parcel shelf.