At least in Windows version of endnote x7.3.1 – you get a menu, after rt clicking in a formated citation, and choose Edit citation, then choosing more… from the dropdown menu.
In the attached image you either put the text (with punctuation and text) into the suffix field, OR you put it in the pages field, using an output style that provides the punctuation and text required such as in the one I modified and attached to the previous message.
