Evening Brad,
I'm not an expert, but for opening larger hatches or engine decks, I use a JLC saw blade with out the handle. You can drill a hole in each corner of the item to be opened. You can then drill a few more along the recess in each direction and with the blade in your fingers and using the fine tooth side, begin sawing on one side. then repeat on the other sides. You will probably have a bit of over cut, but that should be easy to fix. There are also small saw blades for the hobby knife that you could use for smaller hatches and such.
I also use an awl with a very fine sharp point and scribe the area with repeated strokes until you are almost through the plastic. After scribing all 4 sides, turn the piece over and reverse scribe the part until it is free. Due to the scribing, if you want to put the piece back in place, you will have to fill it in a bit. If you want to model the hatch open, you should have no probs at all...I hope this helps a little!
Prost
Allen