In Configuration Utility, it is possible to edit Data Processing of a Layer and observe live changes in Layer's Preview before even saving the Layer. This feature can be useful for tweaking custom scripts parameters.
Best way to do this is to duplicate a Layer, and open Preview by clicking the "Show preview" button in original and duplicated Layer for easier comparison. Edit one of them to see changes between scripts by opening the Layer's "Data Processing" settings with clicking on the "Pencil" button. After the appropriate EO product is chosen hit the button "Copy script to editor" to tweak the script. After setting the custom script you can immediately inspect the changes in the preview window without saving the Layer.
You can also choose different EO Products under "Data processing settings".
With hitting the button you will reset the layer.
Please note that this doesn't work for the data collections which are not included in the Sentinel Playground application, such as Sentinel-5P, Sentinel-3, Landsat 5, 7 and others.