The entire shelf, with the CD changer attached, is removed by simply pulling it out (but do not yank it - just apply a steady force). However, you need to push the bottom on left side in first - you'll hear it unclip. Also, do not try to remove the rubber mat on top - there's no fixing lugs / screws under it, but its rubber rivets are easily torn - I didn't know that and lost one - the mat is now held in place by 3M tape, in addition to the two remaining legs/rivets.
The CDC is fixed to the shelf by four T20 screws. There's enough slack to pull both the electric and fibre optic harnesses safely out to reach the plugs, without removing the changer itself.
The new head unit, so far, has been great: looks nice, pretty intuitive controls; everything works on the steering wheel - there's no "cross-contamination", when the volume would be affected, if you're not in the music playback menu and touch ± buttons (older units suffered from this); the octa-core CPU is fast; runs cold - the fact that it's half size (behind the screen) helps I'm sure; the instrument cluster displays even more info it used to for CDC - i.e. disc number (SD) and the track number, but now also a min:sec counter; satnav works surprisingly well, with a really quick fix, and I can get used to the interface, although I'm still planning to use my standalone Garmin most of the time - I have a fixed, hard-wired stand for it on the dash.
I'm going to play with some settings, etc this week - reversing cam guide lines (there's a choice); side mirror cam activation - to see if I can assign a steering wheel button, rather than touching an icon on the screen (which is not terribly taxing anyway), startup Mercedes logo, etc.
