Yes, if the gun is pristine with box and papers, being the kind of gun a collector would consider adding to a collection.
Otherwise, if it is a nice shooter grade Blackhawk, then it will simply depend on the prospective buyer, should you later try to sell it. Years, ago, I bought an Old Model 357 that had been drilled and tapped and the job had been well done, so it didn't bother me in the least. I later sold the gun to a friend who didn't care, either. Neither of us planned to scope the gun, but it was kind of nice to have that option. Other prospective buyers, of course, could feel differently. In other words, drilling and tapping may reduce the number of interested buyers. Just means you may have to wait a bit more to find the right one.