Add an existing user as a system user

I'm recreating this topic because someone completely missed the point the first time (https://feedback.courtreserve.com/communities/1/topics/2073-assign-an-existing-member-to-be-a-coordinator).

You can't add an existing user as a system user. When you try to, it makes you enter information as if they are a new user, and it resets their password. I would like to be able to just make an existing user a system user without having to do this.