In effect I changed the coolant because a hose from the climate control was rubbing on the lower radiator hose and wore through it. I had to change the hose, which is an expensive bit of kit being two hoses joined by a block at the centre with another hose coming off. Anyway there were no problems with air locks or the climate control.
You remove the lower radiator hose from the radiator by pressing down a circlip around the end of the hose which can then be pulled off fairly easily, all in all I would say it's an easy job.
Chris