It can be done.
Decompile the model into a scasm source.
Edit the source to make the plane look as you want, i.e gear down, canopy open , pilot not shown, wings folded . What ever!
Finally construct a new scasm source to generate the object bgl. The aircraft model source can be referenced as an include.
Now as for actually editing scasm code. I could spend hours typing out what to do, but unless you actualy get immersed in scasm editing you simply wont understand it. So to keep the answer simple. It can be done, it is relatively easy, (i.e. simple text editing, no GUIs with endless menus and tool buttons). It is however extremely time consuming and boring.