Adding a function to update

Kind of new to C#, or at least to not coding like a dummy. Here’s a question: I have a function I’d like to update every frame, but only under certain circumstances. I could SendMessage from a dispatch every frame, but that seems expensive and odd.

What I’d like to do is: SendMessage(startUpdateEveryFrame) and later, SendMessage(stopUpdateEveryFrame). Will awake help me do that? What are my best practices here?

bool updateEveryFrame=false;

void Update()
{
   if (updateEveryFrame)
   {
      CallYourFunction();
   }
}