This may seem like a basic question to some, however I seem to be having a hard time of it. A while back I created numerous groups of contacts, to which now I would like to add specific keywords. Is there any way to highlight the members of a specific group, and then in bulk to add a keyword to them, thereby making them show up in a contact keyword smart list?

Select the contacts you want (using the 'linked to' column), then go to Menu -> Edit -> Bulk Edit x Contacts.

In the bulk edit screen, you can add a keyword to all those contacts.

I think that should do the trick for you.