OP's original question was can a factory DAO be converted to a double/single action by merely replacing the hammer. That is a frequent question that I have never seen a satisfactory answer to, but here are my thoughts that I hope someone would confirm or correct.

In short, it seems to me that what makes a factory DAO revolver is that the hammer, besides not having a spur, does not have a single action notch. Below is a picture of a 64-6 double/single action hammer where I have circled the notch.



The lock-work on a 64-6 DAO is depicted below. It may be hard to discern, but there is no single action notch. However, the trigger section that would "catch" the notch appears to be "sharp" enough that it would hold the notch when cocked in single action. In other words, I don't think S&W used a different trigger in the factory DOA's than it used in the double/single action revolvers.



So, I would conclude that a hammer switch would work. You may be curious as to why I didn't simply try the switch because I had the single action hammer. Well, I got the hammer after I sent the revolver to S&W fit a new style extractor that I naively thought was simply a "drop in" part. So caveat emptor on my thoughts on this subject!