There was a previous post to add functionality to the TinyMCE editor at [TUTORIAL] Add more functions to the TinyMCE editor! - Hints & Modifications - CS-Cart Community Forums
Unfortunately, I couldn't get this to work for me. I uploaded the TinyMCE 220.127.116.11 as recommended, but when I inserted the code provided, it only caused my editor to disappear. But other people have been more successful with it.
I was able to re-install my old functionality and add an html editor button as follows (as usual, making a backup of the original first is recommended):
In file: /js/editors/tinymce.editor.js comment out:
plugins : 'safari,style,advimage,advlink,xhtmlxtras,inlinepopups',
Insert (from cs-cart v2.1, file: lib/tinymce/tiny_mce_init.js)
plugins : 'safari,pagebreak,style,table,advhr,advimage,advlink,preview,media,paste,fullscreen,noneditable,visualchars,nonbreaking,xhtmlxtras,inlinepopups',
theme_advanced_buttons1 : 'newdocument,|,cut,copy,paste,|,undo,redo,|,bold,italic,underline,strikethrough,|,justifyleft,justifycenter,justifyright,justifyfull,|,bullist,numlist,|,outdent,indent,blockquote,|,styleprops',
theme_advanced_buttons2 : 'formatselect,fontselect,fontsizeselect,|,link,unlink,anchor,image,media,cleanup,|,sub,sup,charmap,|,forecolor,backcolor',
theme_advanced_buttons3 : 'tablecontrols,|,removeformat,visualaid,|,advhr,visualchars,nonbreaking,|,preview,fullscreen,|,code',
Note that I added the html editor to the end of the last line. The Link Add/Edit button is acting a little screwy for me, but other than that it has been problem free.
I hope one these helps.