The WaniKani Reorder Ultimate 2 does allow randomizing lessons:
You just need to use the ランダム option while taking lessons (you can even click on it several times to re-roll the random lessons if you don’t like the ones that got picked)
A couple warnings though:
- In one occasion, the randomized order caused me to take a lesson where the reading explanation relied on a vocabulary from the same level that I was supposed to take before, but I hadn’t.
- There’s been cases of users abusing this script to only take their radical and kanji lessons and ignoring vocab for faster leveling, but hurting their overall retention since they lacked the reinforcement vocabulary provides.