Status: Very close to first vertex editing.
I've managed to save polygon directly reading from polygon table. (Previously I saved it not command by command, but using a stream pre-loaded separately (So you couldn't edit properly).
I've some problem because all gone well if I mantain all the old table values: if I edit a value, from a strange unknown reason the polygon is partially messed.
Need to test with other nsbmd...
Sorry for double, but important.
First actual editing of a NSBMD file.
I used the first model of build_model, editing through the table two coordinates value (For now work only "Const" column.)
Seemed work with simple model.
Edit 19:33: It works also for multipolygon model!