What type of extension for this?

I am writing an extension to insert javascript code after selected textareas to modify their behavior. The extension also copies files to the site and includes a couple of [script src=... ] javascript files in the head tag as well as a bit of other source code.

I am almost done with it as a behavior, but while working on it, there have been a few times when I needed to refresh behaviors and that inserted and onblur or onload behavior into a tag.

This extension will not actually use any of those event handlers. Is behaviors the wrong type of extension to use, and if so which ine would be better? If the answer is server behavior, is that reasonably easy to migrate because the documentation for server behavior feels a bit above me yet...

Thanx,
Steven