Power Bin multiple folder metadata

Is it possible to add a keyword to clips in multiple folders nested in multiple folders? i.e. I have a huge Ghosthack library and I'd like to add 'Ghosthack' as a keyword for each file. There are about 50 folders, many with multiple subfolders and even another layer of folders. It doesn't even seem possible to add a keyword to a whole folder without entering it. I have 160GB of mostly audio that I've been collecting and this organization is looking pretty daunting without having to go into each and every folder.

Help!