The nearside headlamp glass on my 1999 Octavia got broken by a stone last week, it is currently held together with tape, but I need to replace it before it all falls apart. I noticed that the glass apears to be held in by clips, do I have to replace the whole unit or can just the glass be changed? and If so, how easy is it to do? Does anyone have any special techniques or tricks to doing the work? Thanks in advance for your help.

I think you are in luck. Acrylic lens headlight units on post-facelift Octavias are one piece, but the glass lens is listed as a separate item for the pre-facelift model.