If you are talking about in-text citations, then the short answer is no. In-text citations have almost no knowledge of their surroundings. They can't tell if they have been used before or not. The only thing they know is whether they are part of a group
or not, and whether they are at the boundaries of that group or not. They don't even know who else is with them in that group.
There is a workaround though. Nobody is stopping you from writing a macro which does post-processing on all citation fields. You would have to implement your own logic of course but it is doable. Something along the lines of:
For Each fld In ActiveDocument.Fields
If fld.Type = wdFieldCitation Then
' do something
If you are talking about the bibliography, then it is certainly possible, but it will require a good deal of knowledge of XSLT. And if you have to start from the styles which come with Word, it is even more problematic as they are very difficult to understand.
There is very little logic in the way they are build.