You should be fine, such snails normaly do not go very deep, maybe a few cm at most. Should be easy to sift them out with your fingers. The only time disturbing a DSB is a problem is when you get down deep either by your own doing, or by having an animal such as burrowing / sifting gobys, or by having starfish that eat the life in the sand. The snails you have do not eat the life in the sand and only use it for a hiding place. You should see their little "snorkels" sticking up out of the sand as they wait for the scent of food to give them a reason to come out of hiding.
Chuck