[04-Oct-16] Import lead tags
You can import tags and associate them with existing leads. We have added an option to import tags on manage leads page. Note that tag import is different from lead import. While importing tags you just specify email ids of existing leads in one column and tags in another. Here is the help article.
[04-Oct-16] Tag all leads in a list
You can now tag all leads in a list as a bulk operation. The tag action is available as “Tag All Leads” on the List Actions menu inside list details screen.