We change our personal identities all the time not only in obvious ways such as cosmetic surgery, psychoactive drugs, and emigration but even more through personal growth. A university is at it most glorious and exciting when students are confronted with new ideas and visions that forever change who they are.
Contra Tyler, what Kass, Fukuyama and others worry about is not that the demand for identity is too strong but that it is too weak. In their equation, Personal growth + Biotechnology = Velociraptors.
When the demand for a change in personal identity is strong it can have important external effects. You may not want to be a velociraptor but if I change what choice do you have? Or you may simply have a preference (atavistic and irrational perhaps but still a preference) for human beings as they are now.
Tyler makes the mistake, however, of jumping from such and such preferences are important and real to such and such preferences justify regulation/taxation/subsidization etc.
But I have many real identity preferences that do not justify coercing others. I think of myself as a professor of economics at GMU but I do not have an absolute right to my job. I am a friend of Tyler but Tyler gets a say in this too. I understand why the Quebecois want to prevent the use of English in Quebec but I don’t agree that they have the right to do so.
In the same way, I understand that some people don’t want to expand the human lifespan beyond its "natural" limits but I object to their preventing others from doing so just because they don’t like the sight of sprightly senior citizens.