Apply Stereotype sub-menu with MDG

[beginner]

Not sure whether this is the right place.

I have a MDG which defines a Block stereotype. When I have such a Block on a diagram, hover (/click to activate the diagram) over that element and press blank I get my toolbox selection where I once again find the Block which I click in turn. Now, for reasons unknown to me, EA opens a sub-dialogue which offers

• Apply Block Type
• Add Block
• ---------------
• Cancel

Now my questions.

• The sub-dialogue shows an Actor and a Use Case as icons in front. Can these be changed and what do they have to do with Apply/Add?
• Is it possible to suppress that dialogue at all? So far I haven't found a use case for "Apply Block Type". (Probably I should have asked this question first.)

Any hint welcome.

b.