This script embeds a "Swap To/Cc" link right in between the To and Cc textareas inside the Gmail Compose view. It's super handy for those times when you want to hit "Reply All" and then invert who the message is directed towards.

To use, save this script somewhere on your hard drive, then open up a new tab in Chrome and drag the script file in there. When you get the popup message about how "Extensions, apps, and themes can harm your computer. Are you sure you want to continue?" click "Continue" even though you might not totally trust me. You can check the script to make sure I'm not doing anything nefarious.

Please report any bugs! I know this thing is ridiculously fragile, so the next time Gmail gets updated, it might totally break. If you have any ideas on how to make it less fragile, let me know those too.

Credit: I got the initial code for this from Swaroop at http://swaroop.in/tag/gmail-address-swapper, but this is a pretty substantial rewrite from what was posted there.