Is changing the expiry date of fish and shrimp and their country of origin in order to sell them after the expiration of their Egyptian validity considered impermissible (haram)? And does abstaining from participating in that remove the sin, or is it obligatory to leave the job entirely, knowing what is happening?

Forging and cheating are not permissible, as they are forbidden in Islamic law. This falls under false testimony, which is mentioned in the Quran and Sunnah (definition). This includes forging documents and records, changing production dates, country of origin, or expiry dates. "Whoever cheats is not one of us." This act contradicts the principle that "religion is advice." It must be avoided, and one should not assist in it. "Whoever gives up something for the sake of Allah, Allah will compensate him with something better."