Is it me, or did this site used to have a "Re-Tag" button under every question? If it did, I personally found it useful. Why has it disappeared?
It's not you, it used to be there but it's been killed off.
From the Meta Stackoverflow post: Kill the Retag option, use just Edit
Retag is gone. It has ceased to be. The "please go back and click the retag link instead of edit" message is gone. We will (not) miss it.
Editing tags only will result in the same behavior as retag, except for the message (low enough rep will put it in review queue for suggested edits, having the retag questions privilege will make it a regular edit.