I had a moderate sucess mixing 1 qt's worth of powdered goat's milk with 1/2 gal of whole cow's milk...i say moderate because there was definatly a powdered milk taste (was trying to make chevre) So if I were to do it again I would 1/2 the amount of powder. (maybe even less?)
I have not tried it on aged cheese...
It had a nice, tangy, chevre taste, however!