I created a symbol script via the create symbol script command. I'm able to drag the symbol from my common library (though it complains that it can't drag & drop, even though it does). From there I can change the textChars of my smart symbols, but I can't change the stroke diameter or the color of any of the symbols pieces including the text.
Have you tried double clicking the symbol instance on the canvas to open the Symbol editor?
I wanted to change the symbol properties instead of editing the symbol, so I could have instances using different colors.