With those being zoanthids, be aware that they change the equation on nuking the rock and restarting. Zoanthids carry palythoa toxin*, which is one of the most deadly poisons there is. It can kill you, and/or pets, and/or... It also can go airborne if you try and do aggressive cleaning measures.
That's includes if you try and cut/pry them off and accidentally cut them or get a squirt of zoanthid juice in your eye (and get permanent eye damage or worse), but particularly if you were to take the rock out and scrub it in your sink or even worse try and boil it (if you Google you'll find the story(ies) of that happening and people causing their entire family issues).
Not that you were planning to do any of that, but I mention it because a lot of people getting into the hobby don't realize how incredibly dangerous some of this stuff is. Some of this aquarium stuff should have big warning signs on the bag "known to cause death in the state of California",.
The comments about pulling out likely aptasia infested rock are good, but the way to handle nuking it is more complicated when it has things long zoas on it than if it's just relatively clean rock.
* not all zoanthids carry palytoxin, or at least not at levels that freak people out. However you're much better off pretending they all do and will kill you then pretending the opposite