Various modifications can be made to a Boolean after creation, including:
Changing the type with the Type parameter. Note that the stocks and tools remain the same.
Changing the parameters associated with a stock/tool by isolating the stock/tool in the Browser. This allows you to edit the stock/tool using the property grid. Additionally, the stock/tool is drawn in a red wireframe when isolated.
Removing a stock/tool from a Boolean by selecting it in the Browser and pressing Delete, or right-clicking and choosing from the stock/tool node context menu.
Adding a stock/tool to a Boolean using standard copy/paste commands. Click and drag a solid to either the Stocks or Tools folder under the Boolean's node in the Browser to create a copy of the solid inside the Boolean.
By default the geometric topology resulting from a Boolean operation is "simplified" by removing unnecessary edges and faces. You can preserve faces and edges in a Boolean by setting the Simplify parameter to False in the Boolean's Edit Properties dialog box.