how to apply that feature on stroke

Hi,

I need a perfect circle with a specific brush (spray brush, customized) . I know that If I draw anythng with pentool I can apply any brush on that using 'stroke path' . but I was wondering if I can do that with shape layer which is drawn using a stroke. can I convert this shape's path in a way so that I can apply taht stroke path option? Please guide me. Please.