No need to alter the spec to change from OOB Robert.
When you come to cut the canopy from the moulding, do not try to cut all the way through. Instead, ensure you have a new blade in the scalpel, and gently score, repeatedly, around the cut lines, until the canopy comes free. The edges can then be very lightly sanded.
Attach the canopy with PVA, or a clear canopy glue, for example, Humbrol Clear Fix.
An easy way to paint the frames, rather than mask the relatively flexible part, is to lightly lay down some clear parcel tape (3M Scotch tape) onto a piece of glass, Paint the interior colour on to this and, when dry, paint over this with the exterior color.
Cut the tape into strips the required width, and then attach these to the frame lines, burnishing them downs o that they stick firmly.
Alternatively, mask the canopy and paint the frames before cutting it from the mould form.