The wing tips on many light airplanes are NOT structural at all -- they are merely plastic covers that also hold the nav lights. You may well damage them if you push too hard on them! IF you feel you must do this, AT LEAST determine where the spar ends, and push directly under the spar AFTER any tiedowns are removed!
Especially if the airplane is tied down when you push on a wing tip, you may induce loads that are beyond the design parameter of the wing. The wing is designed for a load across its entire surface, not concentrated in one spot at the tip.