I assume you mean you have a file cabinet containing vendor-related documents, and one of the indexes on those documents is the vendor name? So, when a vendor name changes, you want all the existing vendor name indexes to change to the new name?
If that is the scenario, I would need to understand how DocuWare would be made aware that a vendor name had changed? Unless there is some database trigger or automated lookup, there is no way for DocuWare to know a vendor name has changed in whatever system you are referring to (ERP system? Purchase Order system?).
At this point, it would seem the only way to change all existing documents would be to bring up all documents under the old name and then bulk-change the vendor name on documents in the result list.
If you have a more sophisticated DocuWare module such as Workflow or AutoIndex, I would guess you could perform an external lookup to try to catch vendor name changes and then have the indexing process change old indexes. Even that process, though, would need to know the old and new name to perform a change.
None of this even gets into the fact that you will then have documents in your system where the vendor name on the document does not match the vendor name in the index. But I assume you are operating under business rules as agreed upon at the DocuWare site..