Don’t know if this has ever been noticed before (if so I was never aware), but I’ve just discovered a visual change on the blu-ray for ROTS: added moss on the roof of Yoda and co.'s platform on Kashyyyk. I just happened to notice this so my guess is there are probably a few more small alterations like this.
Also, I think the DVD is cropped ever so slightly. But I bet that’s been noticed already.