Gene manipulation has a different effect on each species it's done with. For example, dogs have a huge genetic potential for variety due to the length of their DNA chains. That means that only a very small percentage of their genes has to be manipulated to create a different breed of dog. Since only a very small portion is changed, it normally creates fewer health problems. Very few species have the same genetic potential for change as dogs do. Even in dogs, great care must be taken when breeding pure bred animals to avoid the genetic health problems like deafness, blindness, etc.
Most other species do not have such long DNA chains, which means the potential for variety is not as great. It also means that manipulating the genes/DNA in some species is more dangerous, since the chains aren't as long - changing 1 small thing causes a greater effect in the animal. (Thus a more dramatic effect on their health and longevity.)
I guess the long and the short of it is that some species are more able to be safely manipulated than other species. I hope I am explaining myself that in a way that makes sense.
There is plenty of anecdotal evidence that gene manipulation in Degus is by and large detrimental to the animals. Largely because the genes that cause the different colors are recessive, and recessive genes can often make proteins that are non-functional or less functional than dominant genes.
Maybe with more study of the effect of gene manipulation in Degus we'll know for sure. For now, unfortunately, we can only go by anecdotal evidence.
Comfort if you've lost a pet, or are facing a loss