I would only notify subscribers on Tapas if I changed the actual content of the episode, like a redrawn panel, extra panels, etc. If you notify your subs of an edited episode and they see it's only because you added a "like comment sub" image (if they even notice), then yes, I'd imagine they'd get annoyed, especially if you do multiple in a row.
EDIT: Yes, like Chalk said, when you update an episode on Tapas, a pop up will come asking if you want to notify your subs of the change.
No idea about webtoon.