To impersonate or pose as someone else; to pass oneself off as another person or identity.
犯人は被害者になりすまして銀行に行った。
The criminal went to the bank pretending to be the victim.
ネット上で他人のアカウントになりすますのは違法だ。
Impersonating someone else's account online is illegal.
舞台俳優は役になりすまして観客を魅了した。
The stage actor fully embodied the role and captivated the audience.
To become something completely; to fully take on a state or role (often figurative).
彼はプロになりすまして、素人ではない振る舞いをした。
He acted like a pro, completely taking on a professional's manner.
子どもの前では父親になりすまして強く振る舞った。
In front of the children he behaved as if he were a father, acting strong.