Rule of thumb for aluminum heads

I’m trying to change my thermostat. The issue I’m running into is that the dynamic tensioner is in the way and I’m going to have to remove it. The hex bolt holding the tensioner will come loose. But he Allen key bolt that holds the bracket to the aluminum head will not come loose by using hand strength. I’m worried that if I use any more force to loosen it I could strip the threads in the head. I know it’s very easy to strip threads in aluminum.

Is there any rule of thumb for the amount of torque that would strip aluminum threads? Like if I got a torque wrench to limit the amount of force on it?