Since you use Scan to Home, everyone has the same settings, you cannot have individual settings because you can't modify a template per person, the template is created per login.
So your only option is to do it manually, or make everyone use 400DPI. But if you make everyone use 400DPI, it is very likely they will complain, call Xerox, and change it back.
But if you want, you can change it to whatever you want.
CWIS > Properties > Services > Scan To Home > General > Modify Settings
You probably can't make the change though, you would need admin rights, and your IT would have changed it so the default admin won't work.