Yes, you will probably break the installation of the official level packs if you follow my directions for the pack2 thing.
Actually cg, what I did was copy Level1.lua, to _all_ the filenames in the gamelogic.lua. So my pack1/ contains all the levels that the game could possibly be looking for. I then took that directory and copied it to pack2 _and_ pack3. Since I didn't have the retail version and I didn't know how far to go.
All you'd have to do to fix this to buy the retail levels (If/when they're available again) is to delete your pack2 and pack3 directories (or move them somewhere else - This is of course me assuming that the levels in pack1 that are in themes 2 and 3 will not be loaded from pack1)
After looking at the gamelogic Chunkspy dump yesterday it doesn't appear that anything is missing from the demo except the level scripts for themes 2 and 3.