I'm looking for a series of books that deals with humans escaping Earth and having a mother ship full of humans who are being sent throughout the universe to different planets. The ship can transform the humans into whatever type of alien the planet holds. One set of sisters is transformed to cow-like aliens and sent to spy on that planet. All the while the group that's taken the mother ship full of human colonizers is trying to evade/escape the government people from Earth.
The 9 or 10 humans who steal the colonizing ship drop a couple of humans (transformed to whatever the indigenous species is) to the planet to spy...the end result is to try and overthrow the Earth government. The humans that the colonizing ship transform to aliens cannot be turned back into humans ever again so when they take on the assignment to spy they do so knowing that they won't ever be able to be humans again.