I welcome the comments gents and please rest assured no over-inflated opinion of own abilities (no offence taken whatsoever).....but have come across plenty that have such.
My enquiry simply relates to the need for a licenced engineer to remove a simple 'plug n play' (I use the term loosely) Nav/Comm unit, the majority of which that I have personally come across and presently refer to are held in their tray by one securing screw. No fiddling about with any wiring, etc. on the other side of the tray, just that one infernal screw!
If the repair was a straightforward replacement of a worn item, say a frequency selector switch, and the repaired item is returned with EASA Form 1 saying it has been fully tested and is all OK, then surely the action of sliding it back into place and tightening the securing screw back up doesn't need expert intervention. The EASA Form 1 tells me it's all OK and if it's the same unit going back into the same rack, with absolutely no modifications whatsoever being made, I fail to see why I need to part with several hundred pounds for something so straightforward.