1. If you are admitted to a civil servant, you can't be an impostor, because civil servants have to fill in personal information such as ID number and diploma number when applying for the exam. These are all owned by individuals, and you can't have the same second ID card. When going through the employment procedures, you need to check the information such as ID number and personal appearance. If you are a liar, you will be found out.
2. Of course, if two people are twins, they look exactly alike, and the brother who is admitted to the civil service is willing to give up his position to the twin brother, then there may be an act of impersonation. However, the assessment and examination of civil servants are very strict and are likely to be found out.