I don't use tagging mode for this kind of task. Instead, I use expanded view schemes in the tree. So for example I have a view scheme that shows nothing but "tempo" which is a delimited list. I then simply drag any file into the right list item. Voila. Can be done from anywhere.
To tell the truth, I don't really get tagging mode. I mean, if you sit at your computer with the intention of tagging, then fine. But most of the time (for me, anyway), it's the other way around: I am listening to stuff, then I notice that the tune's tags are wrong or missing. Or I see that 10 tunes need the same keywords tag. The last thing I am going to do is get out of the screen that shows these 10 tunes! And that's exactly what would happen if I opened a view scheme and went into tagging mode. Granted, same thing happens in my method too--that's why all view schemes pretty much have to be expanded in the tree at all times, so that I can always just drag.