Custom node placeholder shape

I’m customising a node in GoJS. Currently it’s a rectangular placeholder.

Is it possible to add new vertex in a node placeholder ?
I’m trying to make a irregular node shape.

Is this a simple Node or is it a Group? Are you asking about a Placeholder or by “placeholder” are you referring to a Shape that is drawn with a dashed line and is resizable?

Shapes can be resizable and reshapable: Polygon Drawing Tool

It’s a simple Node with a placeholder. I didn’t realise there is a polygon drawing. I’ll give a try.
Thank you very much.