I want to be able to make some small manual changes to my bibliography but EndNote keeps overwriting them.
Answer
Wait until you have finished your document completely. Make a copy of it as a back-up. Highlight the bibliography then click the EndNote tab in Word, select Convert citations and bibliography then Convert to plain text.
This will strip out the EndNote coding so you can type in anything you wish.
Warning
Doing this does mean that if you make changes to a reference in your EndNote library your document will not pick up the change so you should only do it when you have finished inserting references and make sure you keep a copy with Endnote coding as a back up. Adding a few words: If you just want to add a brief bit of text before or after a reference you could also highlight the reference, click Edit and Manage Citations. You will then see prefix and suffix boxes where you can add text to appear before or after your reference.