Here's the thing about trimming the blades down.

The blades have a small lead weight near the end. If you trim them down , that weight could sling out of the end of the blade at a VERY high speed. I have had this happen, and the lead weight put a dent in the wall. It will be traveling at an EXTREMELY high rate of speed. That's why I would strongly recommend replacing damaged blades. If that lead weight hits you its going to hurt REALLY bad, if it hits you in the eye or something....well

$15-17 bucks is cheap to protect your eyesight.

If you are determined to reuse the damaged blades, at the very least you should use CA to shore up the end REALLY well. But if it pops out in flight....dont say I didnt warn you.

Not to mention if that weight comes out in flight, that heli is going to go nuts due to a severly imbalanced rotor head.