Printers are so cheap to buy. It would be costly in time and money to modify the P/S to work at 220v. Quite complicated. It is much more easier and would cost less to just buy a 220V model.
However, I notice most HP printers that are shipped with 120V power cords are also capable to run at 220V using a different power cord. You can try this and either your printer will either immediately emit smoke and you will hear a loud pop..or else work perfectly.