Update/Remove tags from products
Product Import Updating - Tags
It is currently possible to ADD a tag to a product via CSV update, however, you cannot UPDATE or REMOVE tags from products via CSV update. The only way to remove a product tag currently is to do so manually, very inneffective when working with a large number of SKU's.
I wish this idea got more traction because it seems pretty important for a large inventory where tags are updated in bulk.