Rosetta now comes with the DCReplacePlugin. This plugin can be used to do a 'Find and replaces a DublinCore field value'.

This plugin is located in 'Plug-In Management | Bundled' 

I suppose a thing that you need to be aware of is that the replace action is actually a 'delete' the old data and 'add' the new data.

This means that the updated DC field where it may appear in the middle of the DC metadata prior t the change will appear at the end of the DC metadata. 

This may not be a problem unless you have ordered your data in such a way t make it readable. For example, we have two dc:rights fields that we want our customers to read in a particular sequence