After a few tries:
The script edits the name and colour, but does not create a new style if I need it. So I don't need the same thing as right-clicking on the style line in the properties panel.

But... when I right-click on the object name to open the dialog, I can edit the name of the selected object, not the name of all objects that have that name. So I can create a new name.

So right clicking on the object name and right clicking on the style name do not have the same effect on editing or creating.