Can I send a tag shown below a question into the ignored or interesting tags set without having to type the tag into the appropriate text boxes?
I can single-click eliminate a tag from either the ignored or interesting sets, but can I add?
Now you are able to do this, to a limited extent.
Whenever you are viewing the questions list filtered by any tag, hovering over any tag on a question will give you a drop-down with two options. The top option will be to add or remove the tag from your interesting tags list, while the bottom option will be to add or remove the tag from your ignored tags list. Whether it is add or remove depends on whether or not the tag is already on your list.
You needn't be filtering by an interesting or ignored tag for this to work - all that is necessary is that you are in a pure tag search, which will have a URL prefaced with
http://stackoverflow.com/questions/tagged/. It will not work on the plain questions view, or in any search with terms that aren't tags (even compound searches).
Wildcard interesting/ignored tags cannot be added in this fashion, but some circumstances allow you to remove a wildcard from your list.