What do you do with Kanji you don't want to repeat because you have mastered them?

I don't really want to delete them from my stack, but it would be good if they could be set to "learned" so they won't show up in the due cards.

Is this maybe already possible?

The idea behind SRS is that you will only see the card again when the algorithm thinks you're likely to forget it anyway. If you're so good at that card that it really doesn't need to be seen for awhile, keep hitting easy every time it shows up and you will very soon not see it for years at a time.

Yesterday I saw my first card come up with a 1 year time for the next review. No need to set anything to 'learned.' I actually found I forget a few at about the 6 month review mark, so they need to be kept alive.

If you answer "Easy" on cards at the last box, they'll come up again after a full year. If you get to the point where all RTK kanji are in the last box (2042 kanji until the 5th edition I think, and a couple more for the latest one), and if you keep remembering them and answering "Easy", at some point you should end up reviewing an average of 6 cards a day.

The hard part is being constant until you reach that point.