A scientific "theory" is the end game in science, it doesn't get any higher than that.
Sure it can. There is a step above theory. Its a scientific law. Thats why you have Newton's three laws of motion. They are not theory, they are indisputable. Scientific theories can be fairly iron clad, but not necessarily irrefutable. That is why they are called Theories.
Newtonian laws of physics were broken by Einstein. They're mostly correct, but the math doesn't quite work.
Theories are understood to be more malleable things, and in the case of evolution, much more complicated and more detail is being added all the time.
While Newtonian physics has been replaced entirely (at least as far as the idea of "truth" is concerned), except it is still taught, and used in engineering, because it's almost correct.
Theories and laws are apples and oranges. An apple will not become an orange, and a Theory will never become a law. They are fundamentally different things, and one is not "above" the other.