When I save my modified models in MED, all my previous changes are cleared
and the "undo" button is grey out. Is it possible to allow me undo previous
changes after save? It is a nightmare when you've done alot of changes to
the model and you can't see the updated model without save.

You´ve got my vote!

Thanks for your support fogman.

One more thing is when moving vertex/face, I can enter
x,y,z value in the field box at the bottom, but didn't
have this luxury for rotation and scale. Would be nice
if you can add it also.

That is a good idea.

by White_Wolf

In the case mentioned above you still have the automatically
created backup file, with the old status of your model.

Yes, but what if I want to reverse last 5
steps out of 10?

The greyed out 'undos' after saving nerves!
You've got my vote, too!