Modification of rimless lenses

I have a pair of rimless glasses that I'd like to re-shape slightly. You can see photos of them, along with the proposed cuts, here: (You'll have to copy/paste the line below in to your browser.)
What kind of tool would I use?
How far can I cut/grind before it would affect the optics?
Do tinted lenses have the particles mixed in with the plastic? (I'm wondering about the potential of chipping any film there might be.)

Thanks.