Creating a Plugin to Replace Quicktags

I wanted to add a new quick tag to the html editor when i’m posting an article. I was able to easily add the button by going into “wp-includes/js/quicktags.js” and adding

edButtons[edButtons.length] =
new edButton('ed_audio'
,'audio'
,''
,'</a>'
,'z'
); // special case

This adds a new button called “audio” and with some other javascript code, it does everything I want.

My question is, does anyone know how I could create a plugin to do this. I think it is generally a bad idea to edit the core wordpress files for a bunch of reasons (including that I will have to modify the quicktags.js file every time a new version of wordpress comes out) so i was hoping that I could get the same result with a plugin.

Is this possible?