Direct Pitch Editing
The Pitch Deviation parameter can be edited directly in the Piano Roll.
While modifying pitch deviation via the parameters panel normally allows drawing curves that are added to the base pitch line, editing directly in the piano roll lets you modify the actual pitch values instead of just the additive layer.
Modifying the Pitch Line
Select Pitch Edit mode from the top of the Piano Roll.
The pencil tool can be used to draw pitch deviations directly on the piano roll.
Selecting the pointer tool allows creating and dragging of points, just like in the parameters panel.
The Simplify Parameters option can be found under the "Modify" top menu (default Alt+S).
This function reduces the number of points in a selection to smooth a curve, at the cost of precision. The resulting curve may not match the original exactly.