Nature has already done that for you. Behold:
This is the Adenovirus:
Adenoviruses (members of the family Adenoviridae) are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double stranded DNA genome. Their name derives from their initial isolation from human adenoids in 1953.
They have a broad range of vertebrate hosts; in humans, more than 50 distinct adenoviral serotypes have been found to cause a wide range of illnesses, from mild respiratory infections in young children (known as the common cold) to life-threatening multi-organ disease in people with a weakened immune system.
One method of gene experimenting and therapy is to find an adenovirus that can target the cells you wish to modify. Then you replace the virus genes with the ones you wish to insert on the cells:
Adenoviruses have long been a popular viral vector for gene therapy due to their ability to affect both replicating and non-replicating cells, accommodate large transgenes, and code for proteins without integrating into the host cell genome. More specifically, they are used as a vehicle to administer targeted therapy, in the form of recombinant DNA or protein.
So just find some that can attach to skin cells, grow them in a lab, then replace their innards with your intended genes and let them have a go at your
Wish to change a skin color? Use genes for some pigment. With thicker skin? Use genes for extra skin fiber. Etc, etc.
I believe this will not do for reversing aging, though. For that, try stem cells instead.