Assuming the diesels have plastic bodies it would be pretty simple. Gut the existing electronics and install a Cruise Commander. Add a Railsounds board if you want sound. You can use the existing couplers on the PS1 engine but you will have to replace the ones on the PS3 engine as their impedance is too low for TMCC electronics.
Metal bodied engines including steam, you have to deal with an antenna issue but with plastic its not a problem.
Pete