I don’t use Mendeley, but if the citation in the document can be represented as below, endnote will be able to match and update the citation.
[firstauthorsuname, Year unique identifier} (I use the PMID as the unique identifier, which is downloaded from pubmed into the “Accession Number” field) Endnote can be also set to use this identifier in temporary citation preferences (see attached image for that menu).
multiple citations are separated by a semi-colon inside the curly brackets.
I keep auto formatting off - until I want the endnote generated citations. Before sharing back with a Mendeley user, ensure that you have reverted the endnote citations/bibliography back to “unformatted citation” (NEVER TO PLAIN TEXT!)
also keep backups, as if you forget and the fields get erased, you can ask word to do a compare documents and get the unformatted versions back, using judicious accept and reject during the word review changes process.
