Hi miclo,
There are some examples in the online script documentation. You can use loadPreset or loadPresetAsync to load a layer preset then remove the old layer and append or insert new layer.
You can also use the Sample Selector template that’s used by Hot Brass, Studio Strings or Skylab instruments. Check one of those instruments to see how it’s done. The advantage of using the sample selector is that you don’t need to write the path of each layer preset into your script, it works like a preset browser.