That really depends on the airplane. You shouldn't damage it, but without any insight into the specific airplane and it's construction, where you're pushing or pulling, if it's tied down (makes a difference for leverage and bending moments),etc, it's hard to say.
Generally speaking, if the airplane isn't strong enough for you to grab the wing and give it a shake, you might consider finding another ride. Where you grab and how you do it, however, as well as the specifics of the airplane you're grabbing, do make a difference.