I spent a very satisfying four hours cutting a big hole in my airplane. In this case, it was the large access door that will allow access to the back of the instrument panel from the forward baggage compartment. I drilled the mounting hinge and spacer strip to the bulkhead, and also to the door, then removed them and began cutting the bulkhead with a Dremel tool. Once that was done, I filed the edges of the resulting hole to within about 1/8" of the cut-line. I clecoed / clamped the door in position, and cut the hinge pin and formed a bent handle on one end of it. The door will be secured with #8 pan-heads screws and platenuts. I thought about installing camlocs, but for the number of times I'll have to open this door, there's no sense going to all that trouble.
Next, I measured, marked, and cut out a rectangular hole next to the rear seat map-light hole for the on/off rocker switch. I'll have to enlarge the hole slightly for the best fit of the switch.