I thought changing the cable was going to be a nightmare but only took me about 30 mins in the end, unlike the garage which charged me £90 to fit a cheap one which snapped a couple of months later! Make sure you get a genuine renault cable though.
Tie a piece of string to the end of the old cable inside the car before you pull it out (if this end has broken you might need to take the cable wire out of the housing and feed it in the other way so you have something to tie it to). When youre fitting the new cable through the bulkhead tie it to the string and get someone to pull the string and look for the end coming through inside the car whilst you push the cable up from underneath, might take a bit of fiddling but as long as youve got it tied to the string it shouldnt take too long.