3rd Gen 12V Always on

I would avoid the nonlinearity in the overall circuit resulting from having a voltage drop across a diode. For something like a vehicle I'd wire it up deliberately, one way, that works one way and is well considered. Having 2 fuses, diodes, etc. for this purpose adds a lot of complexity beyond what might be immediately obvious, e.g. unexpected voltage differences causing unexpected currents such as the backfeeding above which drove a stereo. Cheers.

One example of a possibly unexpected current is if you add a diode (and assuming you keep the fuse vs. replacing the fuse with a diode), now you are in a situation where the 12V can oversupply current to devices and possibly damage/melt/ignite the structural wiring. Guessing the sunroof is 25A and isn't the 12V socked 15A, now you are giving something like 40A to the socket wiring.

 

(plug-in) Blocking or Steering diodes are already used throughout our vehicles by Toyota.

What I found interesting in the duel ended fuse adapters is that a diode could be plugged into one end and an appropriate size fuse in the other. So the diode at the end of the duel ended fuse adapter at the source 12VDC and a fuse at the other end of the duel ended fuse adapter with the OEM fuse removed from the original source. All very accomplishable by most anyone willing to plug in fuses. Not limited to the current discussion of all the time power to the CLA.

Notes:
There is no Relay associated with the Sliding Roof. Ref. your posts #2 & #10.
Are you sure you want to power a circuit with a 20 Amp fuse that Toyota designed for 7.5A or 15A use? They are getting really cheap these days in reducing weight. It is unclear to me if the CLA circuit in use is the P/Outlet No. 1 or the USB. I've never taken the time to distinguish which is which.

If it is P/Outlet No. 1 - that fuse back feeds into the ECU-ACC fuse. So that would explain the radio.