Yeah you can do that, I've done it to mine a few times, check the folding rig link in my sig and you'll see i had to do it for some of the cables. Better to replace the entire length of cable though from the psu...if you're going to void the warranty anways.
Just be carefull poking around in the psu, can be hazardous.
Otherwise, as slay mentioned, an extender is probably a better idea if you're not looking to do a bunch of other work. I usually end up sleeving my cables at the same time.