Hi,
1. Sure, I can try. Please make a full site back-up first and then let me know if I can proceed. If I make any mistake the files may not revert and a backup must be used. Very unlikely, but better to be safe.
2. It’s a bit more complicated unfortunately. Taxonomy term grouping uses taxonomy terms to group the post type results, and wherever it’s not applicate it’s placed to the “other group”. User results are not post types, so they automatically go to that group.
I can maybe suggest a custom code to alter the groups, but I can’t promise anything.