I principally understand what you mean but I do wonder what your desired outcome would be mechanically in this situation? As Bunpro already only fails by one step rather than going back to SRS1, if you just want to see it a little more often, you could just fail it. Going -1 does not really leave room for a “half fail”…
Or you can just go and create a ghost, or set the term to a different SRS level manually, even.
Well, what’s the difference between “hard” “good” and “easy” in Anki etc?
Typically “hard” gives you approximately the same interval (something like 1.15x), which would correspond to leaving it at the same Bunpro level.
“good” increases the interval 2x-3x, so that’s approximately Bunpro +1 level.
“easy” increases the interval 4x-8x, which I think would be a really important option to cut down on review volume for anyone returning to study, or migrating to a new tool, or resetting.
But then again, all conversation about SRS is predicated on intervals for the same card, whereas in Bunpro only ghosts and custom sentences are “the same card”. It’s an open question which intervals would be best for introducing different sentences related to the same grammar/vocab.
I gave up ghosts a long time ago. Just let the natural falling down of the SRS level (and accordingly the natural shortening of the review interval) eventually find the sweet spot you need to successfully relearn the card.
This will depend heavily on how many reviews you are doing of course, but for myself I have thousands of vocab cards in Bunpro. Ghosts would absolutely eat up any time that I should be spending on new material. I trust the learning to come with time, I don’t want 95+% flashcard accuracy, I want to learn a language. Can’t do that if you’re not studying new stuff.
I recommend tweaking the reset to SRS1, too. I remember grammar better ever since I did that.