You can usually take the bulb from the new housing and put it in the old housing. This voids your warranty, but bulbs usually last just past the warranty anyway
This can be done with no soldering 95% of the time. Just a nut on the back of the bulb, and a screw on the side. If the wires are soldered to the bulb, you can usually just remove the bulb with the connector attached. If you feel like screwing around with it, you'll find it's very easy. Just make sure if you touch the bulb, you wipe it off with alcohol to get the finger-oil off.