even the 3.0 X5 has pre and post cat O2 sensors. (should be 4 in total, 2 before catalyst and 2 after.)

Unless the post cat sensors are throwing a code I would leave them as they don't make any difference in fuel economy nor do they make any difference in performance. Post Cat o2 sensor only monitor catalyst efficiency! Save your money unless you Really want to do it!

You won't need to have them reprogrammed, and you'll only need to reset an engine light if it is on. Other than that I'll leave the diagrams and instructions to someone else that has them.