Skin elasticity, you can change this, but you have to be on a rather high level of operating and quite powerful to accomplish this. You will also need Valefor's help with this and will need to offer Him a lot of energy.
This also has to be done piece-by-piece with areas of skin (centimeters) so it can be awkward.
Speeding up hair growth isn't that difficult and can even be done with supplements.