Changing dress sizes at H&M? Doable?

I’m looking to purchase some clothes from H&M but I want to take the clothes in the fitting room, change my top and shorts, and then walk out with them on. The clothes I want to take are a size large while I’m a size Extra Large. I go to a relatively small H&M and the employees don’t know me personally. Do you guys think I would be able to get away with this?