If you're able to reach Screw 26 plus remove it without stripping the head, you'll be able to access Nut 29 and install the bulb. Screw 26 is JIS, of course. Lid 16 is a tight fit due to its order of assembly on the rear fender. So you might have to loosen the nut under the fender to get the lid off (red rectangle). It's essential that you get Lid 16 back fully seated to keep the assembly waterproof.
I forget but there's a threaded brass insert molded in the lid which is easy to free wheel (break the bond) if you tighten down Screw 26 too much to seat the lid. It's best to fully seat the lid and only than tighten the nut that holds the light assembly to the rear fender. This will make the edge of the lid dig into the fender gasket. Something like that. BigBF's pic (bottom) gives the inner view of the license plate snout. In BigBF tutorial, he separated the signal light assembly from the rear fender only because he was fixing the signals and had to access the wires.
