According to this [millenniumfalcon.com], the upcoming DVD Releases of the original Star Wars films are going to feature several alterations. One of the more upleasant changes:
Episode VI: Return of the Jedi:
* Hayden Christenson has replaced Sebastian Shaw only in the Force Ghost shot.
The above claim is further backed by the following post [millenniumfalcon.com], which contains the this screencap:
My question is… why would Anakin’s ghost be young, when both Yoda’s and Obi wan’s ghosts are both old?
Perhaps this is a hoax… but who knows… I wouldn’t be terribly surprised if this has actually been done.