If you mean real ebooks and not pdf or djvu files, the answer is yes.
Simple (generalized) process:
1- Strip DRM, if so encumbered. (How? Exercise for the student.
)
2- Run Calibre ebook management software to convert ebook to rtf or html.
3- Load file into word processor/office suite of choice to edit typos or violate copyright at will.
4- Run through Calibre again to specify cover and metadata before converting back to ebook format.
That will work for pretty much any ebook. There are also specific tools and hacks for some formats (i.e., SIGIL epub editor, etc).
Of course, a quality comercial ebook shouldn't need editing.
