The official site put up an article shortly before the blu-ray’s were released that gave a rundown of all the additional changes for the six movies.
For ESB, the only one I remember off the top of my head was how they digitally fixed the shot where the wampa’s arm is reaching into frame to claw Luke. On previous releases you could see the guy’s actual arm where the wampa arm ended in the corner of the frame. They digitally added more fur to cover it up for the blu-ray, although I seem to recall noticing in the screenshot a parabola* of black pixels in that corner of the image (someone will know what I’m talking about).
I also seem to recall a fix they made to the conveyor belt scene where Chewie retrieves C-3PO from the ugnaughts, but I’m not remembering what it is now. It could’ve been a simple color-timing change for the furnace fire or they digitally added stuff.
Funny how ESB has gained this reputation as the one with the least changes made to it over the years, including '97. But boy oh boy, do I still hear people on the internet talk about how much they dislike the Vader “bring my shuttle” change.
*parabola might not be what the shape is called. Again, someone who knows the alterations well will know what I’m talking about.