Currently, there is no way to disable a script regular users but still allow root to use it, unless you prevent users from installing any scripts (on the Edit Owner Limits page).
However, there is a trick that will allow the script to be installed at domain creation time while preventing users from installing it later. Just select it as one of the default scripts for new domains, and then disable it. It will still be installed at creation time, but won’t be selectable for installs into existing domains.