From FCKeditor Docs

TemplateReplaceAll

This setting sets the default action of the Template dialog window. If set to true, it will replace the current contents of the editor with the template contents. Otherwise, if set to false, the template will be pasted in the cursor (selection) position.
Example:

FCKConfig.TemplateReplaceAll = false ;

NOTE: If the TemplateReplaceCheckbox is set to "true", the "Replace actual contents" will, by default, reflect this configuration setting. Please view the TemplateReplaceCheckbox.