This thread has travelled around the maypole a couple of times. Here is my 2 cents.
Bruiser, in the long run (assuming your time is worth something) it would probably be easier to just buy new 240V 433mHz X10 goodies and sell or toss your US stuff.
Everyone is cautioning about modding the transmitter due to US FCC type acceptance and thus legal ramifications. However if you live out in the bush, you may not give a rip about any of that.
One thing that was only briefly mentioned, and you do need to consider is; changing the module to work on 240V is ONLY component changing and is a fairly simple task. Changing the 310 mHz receivers and transmitters to work at 433mHz will also be component changing (and you will need to find componets similar in size because radio frequency and long leads on components do not mix), however once you have made the component changes the modified transmitters and receivers will need to be re-aligned (re-tuned) to their new frequencies. You will need specialized test equipment to do this. If you do not have the equipment or understand what is needed, you will need to talk to a 2-way radio shop, or a TV repair shop, or a ham radio operator to get the retuning. In other words you will probably be out more money. I don't know if you Aussies have an expression for it, but you may have bought "a pig in a poke".
Good luck