Hi Marc, which version of PRPC are you using? RichTextEditor in Pega 7 is built on top of CK Editor. If you wish to upgrade to the latest version of CK Editor you many have to modify the scripts (like RULE-FILE-TEXT WEBWB PZPEGA_CKEDITOR_EXTRAS!JS). I would not recommend that you do this as this could have potential side effects. Is there a specific reason you would want to do this?
If you wish to use a certain specific plugin you could follow the guidelines listed on the CK Editor Plugin and reference the scripts on the harness itself.