Not an EC135 driver but I do have a few thousand hours in DA42s. For those not familiar with the aircraft it is a simple twin with ECU controlled engines managed by a single power lever for each engine. Additionally each engine has ECU AUTO/B switch which allows for the manual selection of ECU B. Fiddling with ECUs is not part of the immediate action drill on engine failure. Engine instrumentation comes via a Garmin G1000 display.
One 'advantage' of an engine failure in a twin aeroplane is that you get significant yaw in the direction of the failed engine. Indeed, first recognition of failure will probably come through the rudder pedals.
In about 800hrs of DA42 instructing, of which probably half that time has been spent in engine failure modes I have twice encountered pilots, one of whom was a qualified twin driver who was undergoing differences training, who have attempted to secure the wrong engine. On both occasions they correctly followed the identification and rectification drills right to the point they went to retard the 'correct' throttle.
It happens.