No, you can not change the scope easily. You will need to change the model for that.
Can't you use the commands to add magazines and weapons you normally use to give soldiers a specific loadout with this new weapon?
I haven't tried this so I don't know.
Just use the "addmagazine" and "addweapon" command (remove the weapons the unit has first useing "removeallweapons" or "removeweapon" ).
How to use those commands exactly can be found in the
wiki.