If I put a div in the head and display:none, than use JavaScript to display it, will this work?
Edit:
I have stuff loaded in AJAX. And as my AJAX changes the "main" portion of the site, I want to change the meta-tags as well.
Yes, it is.
E.g. to set the meta-description:
document.querySelector('meta[name="description"]').setAttribute("content", _desc);