I think this is a fine idea and, no, it will not cause any damage to your bow. Also keep in mind that the efficiency differences between a 60 pound peak weight bow and a 70 lb bow set at 60 pounds are not typically all that great. I would be surprised if it were more than 4-5 fps tops...and not that much on all models. Even noise levels would be roughly comparable. Case in point, I am shooting my Diamond Triumph at a 65 pound draw weight (70 pound peak weight model) and am still getting very good numbers from it and it exhibits very low levels of noise and vibration.

I am also shooting my Bowtech Old Glory at a 60 pound weight (70 pound bow) and that bow is putting up numbers that anyone should be proud of (286 fps- 30.5/60/380). I believe that the type of limb pocket plays a big part in this. The newer Bowtech models all come with pivoting limb pockets whic allow the entire pocket to move with the limb when the draw weight is either increased or decreased.

Shooting at 60 pounds ona 70 pound peak weight bow is fine.