in case I will mistakenly add too much engine oil in the future....

so if the engine oil level is up to H or more, what can you do to decrease the engine oil? if it happen in your own garage that you can't bring up the car to lose the nut and let some oil out...

 

Depends on how much more. If it's just up to the H, no big deal. If it's above by 1 X, still no big deal. If it's beyond that, don't rev it too high till you can get the car to someone who can take the plug out and let some oil out. The problem with having too much oil is that the crank beats the oil in the pan into a froth when it's spinning. Frothed oil doesn't protect very well. You'll also get much more oil going out the crankcase ventilation system and getting burned up in the engine.