Flying your CPL skills test on the DA42 will not compromise your CPL, ie you will not be restricted to only EFIS aircraft.
If you do your MEP class rating on the DA42 then you will be restricted to single power lever aircraft until you differences training as you would for any new twin you fly.
ie you get offered an air taxi job on a Cessna 421 , you do differences training to cover, Turbo charging, pressurisation and 6 lever operation.
