• Download JCE Custom HTML plugin from GitHub (I also saved a copy here.)
• Open / extract the jce-custom-master.zip file and edit editor_plugin.js (located in plugins\jce\editor-custom).
  •  Modify html variable on line 8 to include HTML/Text of your choice.
    
  • Save the modified editor_plugin.js file back into jce-custom-master.zip.
    
    
• Instgall jce-custom-master.zip as a Joomla package.
• In Joomla back-end go to Components >  Editor Profiles > [profile_name] > Features & Layout and drag JCE – Custom HTML button to the Current Editor Layout.
  

June 2018
Joomla
JCE Editor for Joomla