[Stig Eliassen]

Hi.

When you say "diamond" I guess you mean the top of the velocity stalk. There's one velocity diamond for each note, no matter how long the note is. You can't "insert" another velocity stalk for the same note. One note equals one diamond.
You can however insert virtually endless amounts of breakpoints in the volume track view in Pro Tools. This is known as volume automation. There you can insert a breakpoint in the middle of a long note, and just fade it out. You should seriously consider reading the reference guide chapter 23 "Midi Editing". This guide is very well written. Just take it slow and you'll be fine.

Once again....one note = one velocity stalk with a diamond on top.
Good luck.