DON'T DO IT! sheesh, what a pain in the arse.
For starters it's not a standard cable. I though it was a standard brake cable (1.5mm dia) until I removed it and found it had a stop on the end like a gear cable. I say 'like' because it isn't the same as the stop on gear cable either, it's 3.5mm dia where as a gear cable is 4.5mm dia. "No big deal" you think but you'd be wrong! The cable stop sits inside another part which acts as the main pin to lock the seatpost in its positions which has an internal dia of 4.1mm.
That elbow joint on the 2013 model which allows the cable to exit parallel to the post actually bends the cable round a pin only about 4mm in diameter. It's under a pretty high tension so the cable is being bent past its elastic range and has a kink in it because of this. This is important because when you pull the cable through the elbow as I did you end up with a piggy tail of a cable in ball of mess. Sadly I didn't realise this at the time and just assumed it was a poor quality cable and thought it would be better to replace it with a gear cable....
..So out came the drill. I drilled out the main pin so it would take a gear cable and then set about trying to thread the cable back through the elbow. I spent ages trying to work out how to get the cable through using various guides, bits of wire, pliers, scredrivers, etc. In the end I had to hammer the pin out of the elbow to do it. You also need to put a bend in the cable at the elbow or you can't get the pin back in.
The downside of drilling out the main pin means the tiny plastic cap which slides up and down the post no longer fits. In time I guess this means the metal on metal rubbing might cause some wear but it seems to still work ok. Given the spring pressure on the pin I doubt the plastic cap would last very long anyway.
So as you can see the cable can be replaced but it is far from simple!
As others have said the rest of the construction is very straight forward. Several people have mentioned the need to strip and grease it but the main spring in mine was lathered in grease so I just put it back in.
Anybody want to see pictures? Won't bother posting them otherwise.
Hopefully it saves someone the grief!