If I find that the dose is more than required for the correct level I generally unload the whole basket back into the doser and redose to the right dosage for the correct tamp level. Yes, I find overdosing and tamping harder to get to the right level will effect the shot. I think there is some allowance if its just a slightly harder tamp but if its a significant more pressure on tamping to get the right level it will generally cause some issues.
Did you try my rice test method for tamp level? Curious how it compares to your current tamp level.