This is a probably a good feature request- to have the cram section based on book path, not just JLPT. This is what the cram feature is for, it doesn’t seem economical to remove your N5 grammar from your normal reviews. However under cram, you could select the levels > studied grammar and start selecting for cram based on the book (tedious, yes and not faster than what you are doing but you don’t have to reset any reviews). I see mostly N4ish on the path I think.
I also read someone request the JLPT listing for the book paths which would be helpful if available. You may consider just going to your troubled grammar first in cram (even outside of MNN2) just to find your challenged areas and prioritize. Good luck on your exam!