Use the "Edit and Manage Citations" button on the Word Toolbar to change how a formatted citation appears in Word, or to add a page number inside the citation.  

For example after inserting a citation

(Author 2010)

to change to

Author (2010)

1.  Highlight the citation in Word

2.  On the EndNote Word Toolbar, Click on  "Edit & Manage Citation(s)"   (or simply right+click on the Citation)

3.  Select "Display As: Author (Year)"

4.  Note: This will change the highlighted citation only, others will be unchanged.