It should be possible to do this by updating the files in the editor source by replacing the /editor/ folder in the configuration.
It is in: shared/Webassist/RichTextEditor/Source/editor
Before you do this though you should make sure to back up your RichTextEditor folder in the configuration, in case there is a problem this will allow you to revert without re-installing. If you do not know how to get to the configuration folder here is a link to a thread that list the location of the configuration folder for various versions of Dreamweaver and the OS you are using:
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