Intercepting 'set the script..." in the IDE editor

[Dar Scott]

I want to make a plugin that makes some tweaks to a script just before it is applied.  I want the user to see and edit his version, but what is saved is a slightly different version.  

In some ideas, both are valid scripts, that shown in the editor and that put into the script property.  In some ideas, the edited one is an extension that might not color right or give the editor grief, so I'll put off those.  

In many cases, I can limit this to intra-line changes only.

Is there an established way to do this in the standard editor?

In plugin notes, I see only a message that is sent when editing starts.

(I tried changing the script outside the editor, but the editor complained that it was changed and then froze.)

This might be used in things like constant folding and macros.  

Dar Scott