The "KEY" is the special tool that most people seem to be missing.
It is used for unlatching the tonneau cover, and removing the lower right grille insert for access to the towing point.
( You can get by with a thin 10mm open end wrench and a long screwdriver )

I went out to the garage and had a look at my top, there is no way to access the 2 side locks when the top is locked down except possibly removing the plastic trim ( around the top of the windshield and the visors )
I do not know if this trim can be removed with the top locked, and I am not really sure it will provided the needed access to the locking mechanisms if it can.

Sorry, that's about all the help I can provide without trying to remove the trim on mine, and I do not wish to break anything in that attempt.

From the service manual, it appears it CAN be done :
1. Lower the convertible top. ( EXCEPT FOR MAYBE THIS STEP .....
2. Remove both A-pillar trim panels. (Refer to 23 - BODY/INTERIOR/A-PILLAR TRIM - REMOVAL).
3. Remove both sun visors.
4. Remove the dome lamp assembly.
5. Remove the lower windshield trim panel and disconnect the universal transmitter harness connector.
6. Remove the upper windshield trim panel.
7. Disconnect the latch retainer switch harness connector(5).
8. Remove the latch retainer bolts (4) and remove the shim (3) and retainer (2) from the windshield header (1).

( the Allen bolt is located top center in the trunk, it is the manual release for the rear bow latch, nothing to do with the header latch )