Thoughts about note input modes

At the moment, there's an on/off note entry mode, which is fine. I was thinking it would be cool to be able to add additional modes, both on/off and multi-choice, within which the user could define what actions happen.

So, with note entry off, pressing 4 means “change the current note to a quaver”.
With note entry on, pressing 4 means “give future inputted notes the duration of a quaver”.

But what if another mode could be created by the user, for example “velocity mode”.
With note entry off and velocity mode on, pressing 4 could give the note a velocity of 40 or something.

I guess this would be like custom shortcuts, but with multiple sets of custom shortcuts, and ways to switch between them by pressing a button or hitting a key such as N.