Smart filtering means that you can readjust the settings of a filter without undoing previous operations, reopening the original image or creating a new layer. It only works in Photoshop CS3 and higher.
Before you can apply BWStyler as a smart filter, you have to turn the current background image or layer into a smart object. You do that by choosing from the menu Filter > Convert for Smart Filters or Layer > Smart Objects > Convert to Smart Object.
After you applied BWStyler by clicking OK on its dialog, you see a BWStyler item on the Layers panel.
To readjust the applied BWStyler settings, double click the BWStyler item in the Layers panel. You can also deactivate the BWStyler effect by clicking on the eye icon at its left. To adjust the opacity and blend mode of the effect click on the icon with the two sliders on the right-hand side of the BWStyler item.