I never worked the -535C, but my recollection is that the engine/aircraft interface didn't change between the 535C and the 535-E4 (just maybe some pin selections for the EICAS and FMC to account for the different engine limits and fuel burn).
If my memory is correct, it's not impossible that a particular aircraft might have switched between -535C and -535-E4 more than once. Aircraft comes in for heavy maintenance, they drop the engines and send them off to overhaul, then install whatever type they have a pair of handy (I'm pretty sure intermix wasn't allowed so both engines would need to be the same type).