Once you have inserted a citation, you should not edit it directly (although you can do so). Direct edits are lost the next time the citation is reformatted.
You can almost always get EndNote to format your citations exactly to your specifications by editing the style, the EndNote reference, or the citation (as described here).
To safely edit a formatted citation:
Click on the citation you wish to change.
Display the Manage Citations dialog in one of these ways:
Double-click on the citation.
From the Control+Click context-sensitive menu, select Edit Citation.
From the Edit menu, select EndNote Citations, and then Manage Citations
All of the cited references in the document are listed. Select the appropriate citation from the list (you can scroll through all citations in the document) and make any of the following changes for the highlighted citation:
Bibliography: Select a different output style to reformat all of the citations and the bibliography.
Minus Sign: Click the minus sign to delete the citation from the document.
Exclude Author: Select this to omit the author name from the formatted citation.
Exclude Year: Select this to omit the date from the formatted citation.
Prefix: Enter text here to print immediately before the citation text (spaces are significant).
Suffix: Enter text here to print after the citation text (spaces are significant).
Click the close button to implement your change(s) and close the dialog.