You can lock the style you are working on and change its properties to get an immediate preview, without the need to switch between styles. Create a multilayered style on your image, with chained styles on each layer.

 

_____Lock the Preview

Select the layer that has the preview that you want to keep visible - in our exemple the bottom layer. We want to modify the Random Painter to obtain different results, but we want to do so without the need to switch between the filters to see the final result immediately. If we would not lock the Texturizer filter, we would have to click the Texturizer filter's properties after each change as the visible preview is the Random Painter's preview. 

So, to be able to see the whole result of the layer, without switching, click the Lock icon to lock the preview of the Texturizer filter. We chose texturizer because it is the last filter of the layer, therefore it is the result. This specific filter will be locked in the preview. 

Select the style which has the properties you want to modify, in our case: Random Painter and drag the sliders in the Properties+Preview pane. The preview you have locked previously will be rendered in real time. We have zoomed in the preview to 1:1 to better see the changes of the brushes.

Change the style's properties as many times as you want, the preview of the layer will be rendered again. 

When you are done, you can unlock the layer and continue working.