If we could change DNA wouldn't we be able to cure certain genetically "caused" (predisposed) diseases immediately? That would be a pretty slick deal, like a "Search and Replace" function in word processing.
While we have made great advances in genetics and DNA, I doubt we will ever see the ability to change all the DNA molecules in animals or humans to the "improved" engineered version. Perhaps we may be able to change a DNA strand in a zygote and pass the improvements onto the next generation, but not beyond that.
I think you are worng. There are already experimental treatments that use viruses to alter DNA in adults. They may not work yet, but the technique shows promise.