Create a simple style as shown in section 2.1.2 "Create a simple style using Layer browser" and select a second style from the Styles tab (E.g. Building Blocks/Simple Styles/Map to Palette). Choose whether to add it above or beneath the first applied style. Drag and drop it onto the layer.  An orange highlighted area appears in the Layer Browser to show if it is above or below the previously applied style. There are three different ways to apply the selected second style to the image:
•    Drag and drop the styles into the highlighted area either above or below the layer.•    Shift + Double Click the style to insert it above the selected layer or Shift + Ctrl + Double Click the style to insert it below the selected layer.
•    Press Shift + Enter to insert the style above the selected layer or Shift + Ctrl + Enter to insert the style below the selected layer.

Note: For styles dropped above or below the previous style, PostworkShop automatically creates a new layer in the Layer Browser since they are applied in parallel and have to be blended.
Select the layer with the properties you want to adjust (e.g. “Map to Palette”), it will appear white, while the other layers remain gray. Switch to the Properties + Preview pane and set the style's properties by dragging the sliders to the desired values.
The Progress Bar shows the percentage completed. You can always cancel the rendering process by clicking Abort or using the Esc key. 

The two styles have to be blended. Choose a blending mode (e.g. "Overlay") and adjust the opacity of the layer if necessary. The resulting image is rendered in real time.
You can add and layer as many styles/filters as you want. For example, add a Sketch filter above the other two layers:

and change the Sketch filters properties such as switching the Brush Type from Opaque to Transparent so you don’t have to blend the layers. And our final result is: