I accidentally dinged the flat side of a condenser lens with the edge
of another lens, made a small gouge probably a couple of 1/1000ths "
deep give or take - I can feel it with a fingernail - and it's quite
visible when projecting an image through it.

Will one of these windshield repair kits with a sunlight hardened resin
make the ding optically invisible - i.e. so that it doesn't cast a
shadow when projecting through it, or is pointless to try? Don't want
to spend the $11 if it's not going to work. Is there any kind of repair
material for this kind of thing?

If that method isn't going to work, it's my understanding DIY lens
grinding is possible. Do you think it would be possible to grind down
the flat side of the lens past the point of the damage? Any links to
directions on how to do it? Where's a good place to get materials to do
this?

I know, the lenses aren't expensive but I hate to waste an otherwise
good one. I assume it would change its focal length slightly but it's
probably not crucial for my purposes.

Thanks for all input.