Assuming the role of implies the act of taking on a position, duty or responsibility. Antonyms for this phrase would be relinquishing, abdicating, forsaking, or renouncing. Relinquishing denotes the act of giving up willingly while abdicating implies giving up a position of power or responsibility without consent. Forsaking entails abandoning a responsibility or duty, while renouncing implies formally giving up a title or position. Other antonyms could include refusing, rejecting, denying or disavowing, as these words suggest resistance or refusal to take on a particular role. Conversely, embracing, accepting, assuming or taking on a role could be seen as synonyms for assuming the role of.