fwiw I've just done this. As stated above it's pretty straight forward, with some caveats, and as usual would certainly be quicker next time through now I know what to do (though I hope I don't need another cable too soon!)
Below is what I found, while I can still remember, for anyone thinking about doing it. Sorry it's a long post!
I bought OEM parts, fine it's more money (~£65 from dealer vs ~£58 from Renaultpartsdirect for the pair) but I wanted to be able to whinge at the dealer if they sent me the wrong ones.
I did it on my drive, it would have been easier on a set of lifts or a pit. I backed onto some building blocks (3 lined up in a row on their sides in each side of the car, high density 100mm tall when on their sides) at the front before backing the rear wheels up some standard Halfords-esque steel ramps, which gave a bit of extra headroom - a few more inches would have been even better though!.
The heatshield under the central silencer needs to come off, really quick and easy (10mm bolts + retained washers, going into nuts welded onto the backside of the other heatshield/bodywork, etc. Spray of WD40 and off they came with no complaints. The lambda sensor wiring is clipped to the front of this heatshield so this clip has to come off to get the heatshield out to give more room (this can be pushed off the edge using needle nose pliers against the edge of the clip & the side of the heatshield). Heatshield comes out most easily in one direction (sideways towards the OS/Right of the car).
I had to (and you will also need to) slacken the handbrake adjustment nut, access isn't great but it's easy once I worked out how - I ended up with a long 13mm socket + a universal joint, then an extension going to a ratchet (socket needs to be long so the bolt at the centre of the adjuster can pass through). Otherwise access is still pretty restricted by the silencer even without the heatshield, so this can be a bit of a pain as you can't turn the ratchet very far. Give it a spray of WD40 before starting.
Moving to the back of the car, the old cables can be pulled out of the hole through the brake calipers quite easily (disengage from the piston actuator - maybe there's a correct term for this component - then give them a yank to pull them out forwards). To get enough slack in the cable that is still intact you'll need to slacken the adjuster nut and/or get someone to compress the brake actuator so it can be unhooked. It should be possible to do it all by slackening the nut, but my Dad was helping so I cheated and didn't need to slacken it quite so much (same goes for fitting the new ones).
Make sure you remember the routing, though when you put the new one in there's really only one way it will go (make sure it goes through the retaining hole near the rear suspension torsion bar). There is also a clip to remove for each cable, which stop them from flopping around underneath the car (though the two are in in slightly different locations due to the fuel tank location). These are both located around about the mid-point of the cable at or around the fuel tank.
If you look at the new cables you can see the push-fit part with barbs, which is pushed (forward) into the back of a bulkhead and then pokes into the region above the centre silencer where the adjuster is. To remove the old cables give them a good tug from behind the bulkhead (i.e. grab the cable somewhere under the fuel tank after unclipping it and pull hard). The cable will probably part ways with the plastic barbed clip, which will remain embedded in the bulkhead. After quite a few tries, I worked out a way to get these out. The actual handbrake cable will still be going through this clip and the bulkhead, so chop one end off (one will probably have fallen off already which is why you're under the car in the first place) and pull the wire out to just leave the plastic tube/clip.
To get this off I popped a long screwdriver in (it won't go in very far, not all the way to the bulkhead) and levered it a few times to loosen the clip/break some of the barbs off the clip. Then I popped one claw of an adjustable wrench into the plastic tube, gripped it hard and tugged and levered. The NS/Left one is more difficult to get access to, so take a look at this and make sure you have something which will let you reach in. You could probably remove the rear heatshield for better access (i.e. the heatshield which covers the pipe from the centre silencer all the way back to the back boxes), but I wanted to avoid this if possible and it worked out ok.
Moving back to the front, if you look at a picture of the region around the handbrake adjuster (above the centre silencer), the plastic fittings which can be seen going into the bulkhead (heading backwards) stay with the car, you don't fiddle with/remove these - the bits you removing are to the rear of the bulkhead.
Starting around about the location of the fuel tank (i.e. at the clips to which the cables were attached), the new cables are pushed backwards through the retaining holes above the rear torsion bar, then looped around to go through the hole in the calipers and pushed through until they pop out the other side. The wire is then engaged in the actuator arm, then you can thread the cable through the bulkhead (where you just had to remove the plastic barbed connectors), clip onto the bottom of the vehicle on/alongside the fuel tank, and push the barbs home. For the NS/left, it might be worth partly poking the cable through the bulkhead before you push it through the retaining hole as otherwise it needs quite a bend to get it in above the rear heatshield (which I did successfully, but thought it could be done better).
Once both cables are through the bulkhead, slacken the adjuster nut as explained earlier (and/or have someone compress the brake actuators to give you enough slack) to allow you to fit the ends of the cable into the adjuster plate. Tighten the nut up to remove the slack and then try the handbrake to give you 4 clicks or whatever the recommendation is (see thread above).
Refit heatshield, reclip lambda probe wiring, all done.
Probably took 3 hours all in to do this from scratch, next time though (God forbid!) would be an hour tops from start to finish.
