I'm not sure I understand exactly what you are trying to do. There's no way to change the slider name while adjusting the slider, so it's impossible to create in zscript the equivalent of the slider at the top of the tool palette (for example).
Renaming buttons or sliders is also tricky. You can do it if your zscript is always loaded by the user and appears at the bottom of the UI like yours does. What you do is have the new name stored in a memory block so that it persists and then reload the zscript so the button is redrawn. But you can't use the same method with installed plugins.