Well, Fighter is a rock infused song. It's full of those growls, and shouts typical of most rock songs. So the strain would definitely return. Which is interesting cause Xtina has said she would have loved to be a rock star, specifically axl rose, in a recent interview.
But this is strain of epic proportions that can cause permanent damage. I mean, I guess it's noteworthy she wants to change it up, but if you destroy your voice in the process, you're not going to have much of a singing voice left in the future.