Add keywords & metadata to multiple folders & galleries at once?

Hello all - Next up is for me to make my site SEO and Smugmug search friendly. I have several hundred photos visible and several dozen galleries on my site. I have poor to non-existent tags for pretty much everything. Is there a way to bulk add in the relevant tags/keywords into multiple pics and galleries at once? Think of a CSV upload from excel. Or third party app/utility/plugin that will do this? It will be EXCRUCIATING if I have to do them one by one.

Thanks!