I know I’m adding to an old post but I thought this may be useful to anyone using endnote now. I put the long name followed by the bracketed acronym in the author section of the endnote reference (to ensure it went in the reference section of my document). The first time I used the reference I inserted the full reference. Following this, if I needed to reuse it and it was in the middle of the text and needed to be author (year) I inserted the date excluding the author and manually typed the acronym before the date but if it was at the end of the paragraph and needed to be (author year) I inserted the date only and then added the acronym as a prefix. This seemed to work OK.