I have a few questions, just to compare how things are in the US compared to an EASA 145 repair station, eg. "trade" (under EASA there's mechanical & avionics) and type ratings etc etc...
Thought I answered the post question.. Any position can be filled by a freaking TOOL that has no further qualifications further than cutting soy beans. There are many AV tech's with military electronical experience on subs etc, those boys do mod's/run wire etc, they can though replace an ADIRU, have a licensed inspector verify it is locked down and move on to the next job. A mechanic can change any part, have the inspector verify everything is torqued to spec and move on to the next job etcetera....
Having said that, usually systems guys, normally certified with an inspector behind them would take a pile of cards requiring ops checks as an aircraft was in or near to post-dock stage knock out all in question during systems checks.
This is in the USA, cards written by the MANUFACTURERS. Each CAA has different standards, the goal of the manufacturer is to make maintenance as cheap as possible.
Having said that it is the responsiblity of the operator to ensure that they maintain an airworthy fleet.