This post is based on my own experiences, and experiences gained from this Stack Overflow question that I asked. Thanks to Toby Samples and Tim Tripcony for your answers which are paraphrased below.
For whatever reason, whether you are having CSS conflicts or a different reason and you want to use a different theme for a certain page and leave the rest of the application alone. The assumption here is that you have a theme that you like for the majority of your application. You have already set that theme in the XSP Properties of the application.