eponymous
just few simple rules I made for myself:
1) Don't be in a rush
2) Don't do it in the late night
3) Take some masking tape and make the accurate labels for each wire, then double check them according to connector reference.
4) Take the photos of each step
5) Try on old PSU first - your new PSU do not want unnecessary pin ins and outs
6) Double check the labels and numbers on the connector before putting pins back
7) Cut the heatshrinks right

You will be fine