What did Mordecai's decree in the king's name permit the Jews to do?

Answer: Assemble and defend themselves

A sealed royal decree could not be revoked, so a new one allowed the Jews in every city to assemble and defend themselves.

“By these letters the king permitted the Jews in each and every city the right to assemble and defend themselves, to destroy, kill, and annihilate all the forces of any people or province hostile to them, including women and children, and to plunder their possessions.”— Esther 8:11 (BSB)