Can I re-freeze shrimp?
For safety reasons, it's strongly discouraged to re-freeze thawed products without cooking them first, as you don't know how long they have been waiting to be sold. Repeated freezing won't do anything nice to the texture, either.

But as you want to get a decent amount, can't you discuss with the grocer to buy them still frozen? If you then transport them in an icebox with cold elements, you should be able to get them in your home freezer safely.