So it is already smoked right? If so I would be really careful on how much smoke you give it and would most definetly have a water pan in there to keep it from getting too dry - I might even spritz it a few times
I'm with Scarbelly on this one ...i would consider injecting it with chicken broth to keep it moist. Also you may want to smoke it in a shallow aluminum pan with a bit of broth in it to baste your breast with. I would go with a lighter flavored wood like apple...cherry or pecan.
Then you don't have to worry about the 40-140 rule, you are just warming it up & adding extra smoke. I would put it in a cold smoker & get the smoke flowing right away. I wouldn't take it above 145. I also think injecting it with chicken broth & melted butter would also be a good idea. Let us know how it turns out.