All theories can be changed, even Einstein's. If another scientist can make a discovery that can add to Einstein's theories, it will be welcomed by the scientific community. Scientists are never finished with experiments, and they will always look for more discoveries. This is the way that the scientific method works.
Yes, Einstein's theories are unchangeable, because they have not been disproven in all of these years. Many people have added to them, and science marches on, but Einstein made some very good theories about basic principles of science and physics. Einstein's theories continue today. He is truly one of the greats, having made an unchangeable contribution to science.
I do not think that Albert Einsteins theories are unchangeable. I think that people will grow and evolve and every year and decade we will get new information and be presented with a new world in a way to the point that old theories, no matter who made them, will no longer be relevant.
Science is not a static thing, and as such no ones theories are untouchable or unchangeable. There have been many scientific theories in the past that have been proven and disproven by other well known scientists. While Albert Einstein's contributions should always be remembered, if a better explanation is found his theories should be changed.
There is no such thing as a theory in science that is not subject to change. If new information, over the course of decades, comes up that refutes or modifies his theories, Einstein himself would be the first to correct himself - after all, he isn't around to do so.