You don't have to re-import your script
at all to see the changes!
All script files are stored in
Program Files\Messenger Plus! Live\Scripts so if you change a file there, Plus! will load the changes. This goes for
any file in your script, so instead of working from some folder outside Plus!, work on your project in Plus!' own folder!
Oh, and enable the script debugger if you haven't already, so Plus! can reload the script when you make changes to your JScript files.