Is it possible to define a custom style for an activity diagram's nodes and switch to it dynamically, like in a mindmap?

Question

In a mindmap, I can define my own style as in

<style>
wbsDiagram {
    .my_style_name {
        BackgroundColor SkyBlue
    }
}
</style>

and I can dynamically change a node's style simply be adding

<<my_style_name>>

behind. But it seems that this technique doesn't apply to the activity diagram. Is it possible to do so, anyway?