You don't need to "modify" a Hasty-Bake to smoke at 225.
The firebox is adjustable on the fly. There is a crank on the side where you can raise or lower the fire while you are cooking. (So you can quick sear a steak, then lower the fire to finish the cook). For smoking, after you build the fire, you lower the firebox ALL the way onto the ashpan. The unit comes with a deflector for the top of the firebox, and you put it on. Then take a disposable aluminum half size pan, fill 1/2 to 3/4 with water, and set on top of the deflector. Adjust the intake vents to barely open, the output vent to about half open, and Voila... 225 degrees. Cook your meat directly over the firebox/deflector (right side) as the other side is noticeably hotter because the air flow pattern changes with the deflector on.
If you are cooking brisket or other meat with lots of drippings, make sure you leave the grease drain system installed. The grates are angled, with a small channel below that causes the grease to drain into a grease cup on the outside of the cooker. Despite what others say, the system works if you just keep the channel clean. The reason I mention this is that they make an optional basting pan that you can install in place of one of the two grates. But to install, you must remove the grease drain channel that causes the grease to drain out of the cooker. All grease then falls to the bottom of the cooker all around the lowered firebox, where it can catch fire. Don't ask how I know this.
I do not recommend you purchase a basting pan.