See how difficult it is to fit the new hub between the drops. It just might prove the need to cold set the stays is not really needed, at all.

If you do cold set the stays, ensure that the stays remain centered to the center line of the bicycle. Also, check to ensure that the drops are square and parallel to one another. Have a look at Stringing Your Frame Set and you will have a better understanding of how to go about this sort of thing.

Hope that helps.