Since I started 700 days ago, once a card became a leech, I left it a leech after forgetting 8 times.
So, let’s say I want to give a card another chance. I would like to set the individual card to 16, instead of the previous 8. Just for the one card in the deck, not the whole deck. How can I do this?
What I do with leeches, is I “forget” them (using the right click menu in the browser). It basically makes it so the card acts like a new card, so you need to learn it all over again. It also resets the lapse count, so maybe this could be a useful method for you too.
Anki will continue to issue leech warnings periodically for a difficult card. The warning interval is half the initial leech threshold. That is, if you have Anki configured to warn at 8 lapses, future warnings will happen every 4 lapses. (12, 16, etc)
So either you start from a clean slate, or you keep it as a leech and you will get another warning after 4 lapses. Seems like a good compromise to me?