Thank you for your answer!

I agree with you about the "spaghetti hierarchy". They 'inherited' the "spaghetti hierarchy" in some parts already because it is an old legacy project.

So in my experience it is less difficult to judge if a subsubsubsubclass already contains a special form element or not, if you take the getter-approach (1). And if your IDE is fancy enough, you almost get this information for free.
At least it is easier to see (for me) than 'subclass removes A,B and adds C, subsubclass removes B again and adds E... now what does subsubsubsubsubclass contain' as described in (2)

Well, the application design is not really a good example for customer related configuration and I would pursue another and less hardcoded approach, too.

So regarding this context I should have asked which of these two solutions is less painful.

And I completely agree: there should probably be an acronym for that! ;)
k