He is famous not for changing his mind but for changing his mind repeatedly on a number of different theories that he himself brought into prominence, and also for how radical and foundational some of those changes have been. My supervisor used to say that he could delineate six distinct "versions" of Putnam. That is unusual in philosophy, but I don't think mind-changing itself is, at least not more so than in most other intellectual disciplines, including the sciences. Of course, maybe I'm just mistaken about the extent to which mind-changing occurs among individual scientists, since I'm not part of that community.

Putnam's change of mind, on this issue at least, was to a large extent prompted by arguments he developed himself, although his "Twin Earth" argument is similar to arguments developed by Saul Kripke for other purposes. I'm not sure about the degree of direct influence.