Is there a way to switch off automatically leveling up?

That happens if you guru a kanji from the previous level after leveling up.

Well they’d have to do the vocab lessons… OP could use Lesson Filter if they really don’t want to do any radical or kanji lessons until they’ve finished all of the previous level’s vocab lessons. To do that they’d have to manually check somewhere (not sure where) to see if they have unlearned vocab lessons and set the radicals and kanji to 0 in the script in the meantime.