I have read your message once again and now I think that attributes may work for you: you can setup "Movies" product class with "Actor name" attribute, and customers will be able to search for specific actors or filter products in the category by this attribute with the product filter form in the left side bar (like on
this page). The only thing is that these attributes won't be displayed as "tags", and you won't be able to specify any number of "tags" per product (only the attributes pre-defined for the product class). Is it what you are looking for?