I have a question about level runs. If I run for 1 time to level 400 without stopping the timer, can I arrange this race in three categories? That is, the time at level 200 when I passed it, 300 by analogy with 200 and 400 at the very end?

If I'm understanding you correctly, the answer is no. The category in question is 1 Hero to Level 100, not 100 Levels on 1 Hero. You can not choose which 100 levels to count. Please look at the rules for the category you submit to if you are confused.

I had in mind the kills bosses runs: Omeet, The Green One, Woodchip, the Rodent etc. If I pass Woodchip, the Rodent, then can I send this race to Woodchip, the Rodent and to The Green One?

Yes, you can. Just remember that timing for each run starts are first click and not at a previous boss. Thanks for clarifying.