Can you convert a standard thermoking reefer unit to an electric standby?

Yes it can be done and there are a few companies that will do it for you. Diesel powered units turn a compressor, so an electric motor can also turn the compressor. Most diesel units operate at 2200 rpm and most electric motors are 1800 rpm so allowances must be made in the electronic controls for the difference in speed and of course how the start and stop cycles are controlled.