Which raises a good point Ken.  The other day I had to change a parking
light in my 98 Regal.  I didn't know the bulb was gone until I was driving
down the road and the flasher was running at double speed.  So - I pulled
into the local Advance Auto and picked up an 1147.

In the old days I would either have had to get down on my knees in the
parking lot to reach up under the fender (never a clean job), or grab a
phillips or a torex driver to take the lens off.  Neither approach are
terribly difficult but one is dirty and the other requires that I have the
right tool with me.  Instead, now all I had to do was slide two plastic
retainer slides down about 1/2 inch and pull out the headlamp module which
gave me clear and easy access to replace the bulb.  Put it back in place,
slide the plastic slides back in that lock it down and head down the
highway.  Every bulb for the front end of the car is contained within the
headlamp module, and access could not be easier.

To the OP's point, if the rear module was secured in a similar manner to
what the headlamp module is, then it too could be a completely tool-less
maintenance point.  It does require a socket to remove the nut that secures
it.  I just don't consider that to be such a big deal.  For those to whom
the use of a socket is a major affront, I would suggest getting a wingnut
and replacing the factory nut with the wing nut.  That'll take care of that
socket wrench issue.  My daughter's old '94 Sunbird used finger nuts to
secure the tail lamp modules.  One could get ahold of a couple of those and
use them in place of the Buick factory hex nut too.