io9 has been using the tag Avengers-4 because the name of the film had not been released (see tag page ) however, the title has been released and they want to start using the tag Avengers-Endgame moving forward but want all of the content to be on the same tag page.

A. add `avengers-endgame` (for readers it would be Avengers:Endgame) tag to all avengers-4 articles

B. redirect (301) to tag/avengers-endgame

C. edit can continue to only use the avengers-endgame tag