All my pioneer receivers use the same IR codes. Can this be changed?

I have 3 and perhaps soon to be 4 Pioneer prologic receivers doing different duties in my home theater. Now, the problem is that I want to control them independently but since they all use the same codes they all react with the same buttons on the remote. Is there any switching internally or other way to change the codes. One option would to get all different brands and that would fix the problem but as it stands they are all Pioneer. Anyone want to trade prologic receiver (Pioneer) for prologic receiver (other brand)?