Replacing Light Bulbs

[65cobra1]

I tried "Search" here plus the same on another forum but must be using the wrong words.

My tail lights are a little dim and I was told that LEDs will not fit my model. It was suggested that if I switch the flasher to the bottom and the running / tail lights to the top, they might be brighter due to their position.

So, I crawl into the trunk, and yank on the bulb holder...No luck...Tried twisting...same.

I didn't want to force the bulb holders because my usual result is "SNAP!"

Do I have to take off the entire fixture to replace or move the bulb holders around? (It looks like there are two nuts holding it in place)

Suggestions will be very welcome.

Thanks, Ivan