Fob receiver unit change?
 

I have a 98 v40 that came with a single remote fob, I have access to a 98 s40 that is being broken that has 2 working fobs, can I swap the fobs and associated receiver unit or is the system more complicated than that?

Id like a spare, but there are limits to what is sensible for an older car like this, Im assuming that buying a spare key is going to be painful as well.