Hi,
You either don't have to create additional fields in Ztable or create a new structure. For the context node, simply delete the dictionary structure; in your case, ZVENDOR. delete the ZVENDOR in context node properties and press enter. Then you can add extra attributes in the context node and your existing attributes still point to the dictionary structure ( for ex: EBELN would still point to ZVENDOR-EBELN)
Regards,
Kiran