Hello Jürgen,
are you talking about ROOT-nodes or CHILD-nodes?
In case you are talking about CHILD-nodes you might meet your requirement by implementing a property binding (determination).
You can find further information following this link: http://scn.sap.com/community/abap/bopf/blog/2015/08/04/abap-to-the-future-my-version-of-the-bopf-chapters-part-5--properties
The mentioned class /BOBF/CL_LIB_H_SET_PROPERTY offers the method SET_ASSOCIATION_CREATE_ENABLED. This might be useful for you.
Best regards
Chris