This is going beyond the obvious group focusing of notes in the Key Editor, and then numerous editing functions.
These require a bit of muscle memory, but if you do a lot of editing in the Key Editor, they can save you time. And due to the nature of Key Modifiers, this isn’t something achievable with Cubase Key Commands, Macros, Logical Editor, Metagrid or Metagrid pro to my knowledge.
Martin sent me these long ago because I was frustrated I couldn’t find a complete list in the documentation. If they are, I would like to get a reference. Anyway, these are from the factory default Cubase 8.5 so if there are any that don’t work today, please let me know so I can check on this end. I only use certain ones. Some of these are basic, but I think timeless as it works in C12.
Double click = Insert a note; the length is equal to the Length Quantize.
Double click, keep the 2nd mouse down, and move left/right = Insert a note + adjust the length
Double click, keep the 2nd mouse down, and move left/right = Insert a note + adjust the length with the Snap on
Double click, keep the 2nd mouse down, move left/right with Ctrl/Cmd modifier = Insert a note + adjust the length with the Snap Off temporarily
Double click, keep the 2nd mouse down, move left/right with Shift modifier = Insert a note and move the Note Start afterwords
Double click, keep the 2nd mouse down, and move up/down = Insert a note + adjust the Velocity
Double click, keep the 2nd mouse down, move up/down with Alt modifier = Insert a note and change the pitch afterwords
Of course, you can do all “combinations” one by one:
Double click, keep the 2nd mouse down, hold Shift + move left/right > Move the Note Start; release Shift + move up/down > set the Velocity; hold Alt and move up/down > change the Pitch; release Alt and hold Ctrl/Cmd + move left/right > change the length with Snap Off; release the mouse > the MIDI Note is inserted._
Greg Ondo covers some of these basics, and at 2:00 is where object selection for Midi Notes starts.