Yes you can store clams in the fridge overnight.
Clams keep well in the fridge when alive and even keep well when alive in water.
Refrigerating the clams will not harm or kill the clams.
It's recommended to refrigerate live clams until you're ready to kill the clams and eat them.
Store live clams in the refrigerator overnight in an open container, covered with a moist cloth or paper towels.
Don't kill the clams until ready to cook and eat and if the clams are already dead then they should not be cooked or eaten because they can contain bacteria.