Yes you can prepare clams ahead of time so you could cook the clams ahead of time and then have them ready to eat or serve.
I've cooked clams ahead of time and then took them to a dinner we had in our community and they were just fine.
I prefer to cook my own clams right before eating them for the freshness however cooking and preparing the clams ahead of time is perfectly okay.
You can precook the clams ahead of time and then pack them back into their shells with the compound butter and then use the oven to reheat the clams before serving them.