Hi John,
There is a project to add functionality to give admins more fine-grained control to edit and reset completions which hopefully will be ready for 2.7 which should address your first point.
On the second I'll file an enhancement request to be able to mark courses in a Plan as "Required", though as things stand usually only Programs/Certifications appear in Required Learning. As an interim clunky workaround you could have a duplicate course containing the same content as the original but with a name marking it as the "must retake" course, add it to a program, and assign the users as individuals. Though this may make reporting a bit more complicated.