I've bought an openevse charger which comes with a IEC_60309 plug, however, this isn't supported in Australia.
I've sourced an Australian (AS/NZS 3123) standard plug and it does look quite straightforward to replace the IEC with the Australian plug.
Do I need to make any modifications to the regulator which powers the relay and Arduino boards to accept 240V?
No changes are required. OpenEVSE uses a Universal Switch Mode power supply and can take any input from 96 - 264v 50 or 60 hz Single or Split Phase.
After you remove the IEC CEE 60309 connect:
Red - Hot
Black - Neutral (Hot 2 for Split Phase)
Green - Earth Ground
Thanks for the help, all working now.
Here is a video of the setup.