This walkthrough covers how to reshape MIDI notes after they've already been placed in Ableton's piano roll. Right-clicking the clip lets you switch between Adaptive Grid and Fixed Grid (30 seconds to 8 bars), which controls how notes snap into place as you edit them.
Stretch a note's start or end point to change its length, and hold Cmd (Mac) or Ctrl (Windows) while dragging to free it from the grid entirely for finer, non-quantized adjustments. Select and drag notes left or right to shift their timing, or drag up and down to transpose pitch.
Every note carries a velocity value, editable in the Velocity Editor by clicking or dragging individual velocity markers. Values range from 1, the softest, to 127, the hardest hit, giving you control over dynamics without re-recording or re-sequencing anything.