Herman will step in for Gonzaga against Roy Nelson, while Varner returns to the UFC for Dunham to face Edson Barboza.
The UFC’s site confirmed the changes late Tuesday night. Verbal agreements are in place for each bout.
Herman (21-3) lost his last fight to Stefan Struve, halting a three-fight win streak.
Varner, meanwhile, is 19-6-1 in his career. He has competed in both the UFC and WEC, winning his last two fights in the XFC.