Hi @chlorophil, while you are in the new grasshopper style wizard, (in the “Parameters” step), you need to set each parameter as “Editable By Object” if you want to change it later on objects using that style from the Properties panel.
If you have already created the style, do right click on it and select the “Edit” button to go through the wizard again.
Let me know if you have any doubts.
Cheers,