I did a bit of a search on car remotes. You can get integrated RF and microcontroller chips. It would probably use something like this. The crystal I mentioned is used to set the frequency that the microcontroller runs at. This would likely be higher than the transmitter frequency.

The microcontroller would then divide this frequency and send it to the RF oscillator which is the frequency that the transmitter would work at.

So there are two ways they could use to change the transmitter frequency that I can think of (if they are using a configuration like this). First is to program the microcontroller for all the remotes the same and use different crystals. This would mean that all of the frequencies inside the micro are changed and so would the transmitter frequency. In this case if you swapped the crystal it may work.

The other option, and probably the most likely is they have simply programmed the micro differently to divide the frequency differently. In this case, if they have used the same micro in both and they have the same pin outs you should be able to swap the micro and it will work.

This is based on alot of assumptions. Like the chip used has internal flash memory of some sort. If you can post up some part numbers from the major chips that could be a clue. Hope this helps.