You can undo up to seven of your last actions by choosing Undo from the Edit menu. After choosing Undo, you can then choose Redo to repeat the original action, which restores the canvas to its condition before you chose Undo. You never need to worry about what an action will do to your icon because of this feature. If you don't like the results, simply use Undo and Redo to restore the icon to the way you like it best.
Each time you Undo an action, that action becomes available to you as a Redo action (up to a maximum of seven actions). Each Redo performs the most recent Undo action. The number of Undo actions and Redo actions that are available to you at any time is displayed in the Icon Editor footer.