There’s a script that will do that for you. Though now that I look, it says it’s unmaintained.
Of course, the override script could effectively achieve the same thing. You’d just have to be more careful to not abuse it.
WaniKani is unlikely to make this an element of the default site, seeing as they list “undoing an incorrect answer for any reason” as one of the things that don’t need to be posted in feedback at this point.