You can absolutely do this.
Assuming you have your tool properly set up,
Go to the jog screen on the teach pendant and access the wobj you're trying to alter by scrolling to wobj and pressing enter.
Scroll to the wobj you want and select 'define'.
Change the object method to 'no change'
X1 and X2 are points along the X axis and Y1 is a third point along the +Y plane I believe.
By default I think the X2 point becomes the origin.
After defining the co-ordinate system of the wobj you can always alter the position of the origin by selecting 'change' instead of 'define' at the previous menu and updating the x, y & z with reference to the 'world' origin located at the base of the robot.