have you checked out the documentation on the
milkytracker site?
Yup, that's a sad excuse because I don't know any effects that could help you with that from the top of my head. You also have
note off and
note cut commands that might be of help. I don't think there's
New Note Action? There are trackers where you can set instrument properties so the old note is cut or faded out when a new note is played on the same channel.
I haven't used fasttracker 2 or a clone of it and am not familiar with the shortcuts and options.