+1 on the sandpaper.
light sanding in an outdoor setup will be fine. G10 is not that toxic.
The resin is epoxy, which, in its fully cured state, is pretty inert.
The reinforcement is glass fiber, which is not good to get in your lungs, but you are only going to roughen the surface. If you are reaching the fibers, you are removing too much material for what you are trying to do.