These settings are stored in the ToolsFile.xml and ConfigFile.xml files in the /RadControls/Editor/ folder.
Configuring these values are not supported with Tandem Server but can be manually altered. However, re-installing or updating Tandem Server will overwrite any changes to this file so you will need to keep track of your changes.
The HTML Editor is developed by http://Telerik.com so most technical questions can be best answered through their forums but we are happy to help if you cannot get the answers you need from them.