There was a
similar thread to this a few weeks ago - go ahead and take a look through it, it may help you out.
One of my own posts from the thread:
"...And you can switch species if you find that your first pick isn't you. But, for the most part, "clan hopping" is frowned upon. However, when you switch for completely honest reasons, no one can blame you for that."
And by the way, changing species or clans won't mess up any RPGs unless you're partaking in one. I don't know if there has been a case where one person has controlled both an Alien and Predator, but as far as I'm concerned, it's not allowed.