I think you can disable an I/O rack. Its somewhere in the "S" bits. I remember way back in the early 90's I had built a system where I disabled all the I/O racks that were not being used. Later they wanted to add a rack and couldn't get it to work. After looking around I found what I had done and turned on the bit. The rack worked after that. I did this using ICOM AI software but I assume you could get at them with the RSLogix software.