UPDATE: Someone sent me their old irbus.sys driver for Windows Media Center Edition. I installed it into the correct directory and rebotted.

Worked perfectly. That means that the learned codes on my Pronto now work perfectly WITHOUT any modification! Evidently this older IR driver had a forgiving receiver that didn't require the toggle bits to toggle.

Thanks to everyone who helped me out here. I'm really relieved though that I don't have to learn to hack hex codes.