posture as (someone or something)
To present or portray oneself falsely as a different person or type of person. Someone posturing as a security guard managed to sneak in and steal a bunch of company secrets. You only studied psychology for a single semester, so stop posturing as some sort of expert on the topic!
posture as someone or something
to pretend to be someone or a particular type of person. Why is the secretary posturing as the manager and giving out assignments? Carla entered the ballroom, posturing as a grand duchess of somewhere or another.