I am looking for the same solution. I think I found the files that deal with those settings but I'm not sure what to edit.
mod/assign/templates/
or
grading_navigation_user_selector.mustache
theme/boost/template/mod_assign/grading_navigation_user_selector.mustache
or
mod/assign/amd/build/grading_navigation.min.js
mod/assign/amd/src/grading_navigation.js
When I try to look for any true/false settings or defaults, I'm not sure what I'm looking at. Perhaps someone can help me get the rest of the way?