Hi, I tried the very same thing but with CKEditor. I was using z3c.jbot which is supposed to be the way to override resource files - though I did not succeed (see my old post). But maybe you can give it a try.
As second option, you can register your own resource directory with the exact same name and bind it to your product layer. Please remark, that you also have to include all the other files which originally reside in the tinymce.stylesheets resource directory.