I was looking at the codebase and realized there is a crude, but functional page that allows to fully edit a SRS flashcard.

The page is not linked anywhere and was made some time back in response to a user request. If there is enough interest I could polish it up.

Key points:

• The page is available at: /manage/advanced, it is not linked anywhere within the site
• As the page indicates it can both add or edit a card
• I'm afraid it works only on one card at a time (please don't be rude and spam the server, if you use a script, please give a comfortable 1sec between requests and just let it run) -- I could potentially add a "range" functionality but the plus side is without range functionality it's much less likely for a user to completely mess up their SRS reviews.
• Take note of bottom of page, for example a "failed" card needs: due date 0 (zero), and fail count at least 1, etc. (I'd suggest to refresh the SRS chart page on another tab just to check your change)
• Take especially note of the indexing : the first box on the chart labelled "Fail & New" is internally known as box 1, and "1+ Review" is internally box 2, etc.

Remember: to add cards (both single and many-at-once), you should really use the Add Custom Flashcard Selection which is much more flexible, and gives you a confirmation list of all the cards being added.

This won't help much if you want to "reset" cards. If you want to "start over", then: 1. delete all the cards (remove a Heisig index range like "1-2000" via Remove Custom Flashcard Selection), 2. start adding cards again.

For users who came back after a long break I suggest instead to go through reviews normally -- but first go to SRS Settings and set the Maximum box for cards marked 'Hard' temporarily to a low box, like box 2, that way any "Hard" answers will almost "reset" a card to a low interval, otherwise cards will just move one box lower, which is still a long interval for cards in the top boxes.

Last but not least please remember as of writing, the website only stores the "common" CJK Unified Ideographs characters (which does include all the standard Remembering Traditional & Simplified Hanzi for chinese learners).