I agree, some of those BS34 L-bracket screws are crazy tight, and you never know until it's too late. So now, I always carefully support the carbs and use a hand impact driver with a very good condition Phillips bit. And I always use a heat gun -- heat softens Locktite.
I've removed several tensioners. Again, use a hand-impact driver. It forces the Phillips bit into the screw head, preventing ruining the head, and the impact helps break the threads loose. And again, if you are really worried, apply heat with a heat gun.