Article relates to
RadEditor for MOSS
RadEditor for MOSS v.5.x.x: You can easily achieve this by isolating the desired CSS Classes in a new CSS file ( for example CustomCssFile.css) and setting the editor's CssFiles property to point to the new CSS file CustomCssFile.css.
Depending on your scenario Web Part and WCM / SharePoint forms scenario (Lists, Wikis, Blogs, etc.) you have to modify the ToolsFile.xml / ListToolsFile.xml, which is located in the /Program Files/Common Files/Microsoft Shared/web server extensions/wpresources/RadEditorSharePoint/5.x.x.0__1f131a624888eeed/Resources/ folder like follows:
In addition to this, the following help articles will be in help:
Defining custom CSS styles Add/Remove tools from the toolbar