Bypassing the menu, these hacks allow one to cycle through weapons and adapters with the start and select buttons (though I wonder how you'd get to your E-Tanks then). What's more, there is an option that lets you start the games with the weapons already acquired. This is particularly neat, albeit not tremendously useful, in Mega Man 2 and 3; allowing you to enter stages with the weapons from their respective Robot Masters, a feat not possible prior.
You can check out more videos like the above from other titles on the Press The Buttons article this is sourced from, as well as info on the hacking process. The hacks are not available to the public yet, but Guy is taking suggestions for the ideal means to distribute the modification. I might also ask him if he can do a hack that turns all the weapons to Metal Blade, and Mega Man has unlimited Metal Blades and he emits Metal Blades any time he moves and he's made of Metal Blades.
Thanks for the tip, Matt!