I would be surprised if adding the page number in the “edit citation” suffix field didn’t work. That is the way I usually add page numbers or any other text and it shouldn’t require any special editing of the style template.
However, to use the “cited pages” field, you also need to edit the selected style in the “citation template” to include the “cited pages” field in the citation, with the appropriate “link adjacent” and “forced separation” punctuation, – all of which can be inserted from the “insert field” menu.
(Author, Year[forced separation]:[link adjacent text]Cited Pages[forced separation])