Sometimes I can tell when my current DM fudges a roll to miss an attack or reduce damage. He has a tell in the specific way he pauses and breathes before announcing the roll, then tries to hurry to the next turn, which only seems to happen when someone is in a life-or-death scenario, but “luckily” survives.
Should I let him know he has a tell? Will it be less fun (or more stressful) for him if he knows I know?
I just personally try to balance things without ever taking away from the results on the dice themselves. The changes of plan you listed are all fair game in my mind for balancing encounters. There’s nothing wrong with balancing on the fly, I just think if you’re at the point of lying about the results of individual die rolls, at that point you’re disrespecting both the players and the game system. There’s risk embedded in the system by design. If you don’t want that, play a different system where you can handwave risk away and railroad events without cheating.
That said, this is all just my personal philosophy about GMing and games in general.