Make sure it has not already been injected. I believe all frozen turkeys available in our stores are injected. I wouldn't add anything to that if so.
You could still loosen the skin and put a mix of butter and herbs between skin and meat. And for sure put some stuff like onions, apples, oranges and more herbs in the cavity.
On my next turkey I'm going to release the legs from the factory binding (if present.) The thigh area is the last part to fully cook and binding the legs down can only delay that.
Pictures when done!