You can only modify brush settings for strokes in the 3D scene. You cannot modify brush settings for strokes painted on the Paint Effects canvas.
To modify brush attributes for an existing stroke
To modify settings for several brushes at the same time (for example to change the Display Percent), select the brushes (see Select brushes in your scene), open the Attribute Spread Sheet, click the Keyable tab, then modify the settings. For information on using the Attribute Spreadsheet to modify settings, see Modify existing strokes.
Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License