If you changed either the special theory or the general theory just slightly, dark matter would disappear completely, I suspect. Actually, you would probably need to change both because they dovetail with each other.
In particular, I note that the evidence for dark matter and dark energy are contradictory. On a galactic scale, it seems that there is too much gravity to be explained by the visible matter, so they hypothesize dark matter. But on the universal scale, it seems that the expansion of the universe is too fast, given how weak gravity is, to be explained without dark energy. So on one hand, gravity is too weak to explain reality. On the other hand, it’s too strong. In my opinion, that shows that it tapers off at a rate that is greater than what we believe.