Why does it say "u'Shlalam Lavoz; b'Yom Echad"? The first letters said "b'Yom Echad
Vilna Gaon: Mordechai permitted taking spoils only on the day of war, in order that others will help Yisrael for the sake of spoils.
Malbim (11): Mordechai wanted that Yisrael not take the spoils; it should not look like this was their goal. However, he needed to write u'Shlalam Lavoz (refer to 8:11:2:2). He changed the order, so that "one day" applies also to the Heter to take spoils. Surely Yisrael will not abandon what is primary (vengeance against their enemies) for the secondary (taking spoils). They will understand that they are warned not to take anything from the spoils 1 . Haman knew that if he writes that the spoils are only on the one day, all will pursue spoils and not kill. Therefore he wrote to kill on the 13th, and to take spoils only after that day 2 .
Why did Mordechai write "b'Chol Medinos ha'Melech"? Haman did not write so!
Malbim: He informed that the killing will be in the entire kingdom. Haman concealed this. He feared lest Sarim not want the destruction of an entire nation. Rather, each Sar will think that it is only for his Medinah. Oppositely, Mordechai wanted all to know that the lot changed to Simchah for all Jews.
