I finally figured it out…
After you’ve submitted your Blogger blog’s url to Yahoo! Site Explorer, you’ll see a link to “submit site feed” or something along those lines.
Submit a “ /rss.xml ” in the text box after your Blogger url. Example:“http://YOURBLOGNAME/blogspot.com/rss.xml”
After this, you’ll be asked to Authenticate your website. If not, click on the little yellow icon in the “Status” column of the Yahoo! Site Explorer where it lists your Blogger url.
You’ll be asked “How would you like to authenticate your site?”
Copy the META tag you’re given, and then go to Blogger’s “Settings,” > then “Layout,” > then “Edit html” tab, > then paste the META tag right after you see the first “head” tag.
Here’s the important part that I got stuck on:
You have to type a ” / ” right before the end of the META tag! Otherwise you won’t be able to save your changes in Blogger.
Example (add the slash in red): <META content=’gibberish-gibberish’ name=’y_key’/>
If you’ve done it correctly, Blogger will save your changes to the html, and when you go back to the Yahoo Site Explorer, you can click the “Verify my site” button (or whatever it’s called) and your site will be authenticated almost immediately. Also, from then on, you don’t have to re-submit Sitemaps of your Blogger site, because it’s on a feed.