read-only new feature

Hi people !

I have a ckeditor with the readonly addon.

I am looking for a way to use the readonly feature but with the possibility of but the text in bold or in italic.

To be more specifique, i'm making a website where some users ( lets called them "student" ) can creat new post with all the ck editor feature, and some other users ( lets called them "teacher" ) can edit those post. But the teachers can't edit the text (read-only ) ,  they  can only underline some of the text.

i hope i made myself clear enought, tell me me if you didnt understand.