Is it okay to change the research area of interest that I specified in my statement of intent after submitting an application for a PhD program? I had submitted my application to the PhD program in Statistics, and in my statement of intent I specified that I would like to do a PhD research in Computational Biostatistics. I am in a Master's program right now and in this my last term I am taking a course in Statistical Learning. The problem here is that, I really like the materials covered in my Statistical Learning course, and now I want to do my PhD research in Statistical Learning / Data Mining, rather than doing Computational Biostatistics. 

I already have exchanged few emails with a Biostatistics Professor at the university that I applied to, but no official contract was made between me and this Professor for me to do my PhD under this Professor's supervision. Also, the policy of this university is that new PhD students are initially not assigned a supervisor, but each new student will be choosing their supervisor towards the end of their first year, after taking the mandatory PhD reading course with a faculty member(s) that the student is interested in working with.

Is it okay for me to change the research area of interest that I specified in my statement of intent after submitting an application for a PhD program?

Thank you,
Under the conditions you state it is perfectly ok for you to change areas. I doubt that it is even necessary to state it prior to a decision being made on your application, since they don't assign supervisors early on. It might be different if you needed to pick a supervisor prior to acceptance. 

In fact, you would be wise to look carefully at potential supervisors now and after you arrive to be sure you have someone compatible who does work you are interested in. 

However, just as an option, you might want to correspond with the professor mentioning your "broadened" interests and asking for advice. I wouldn't claim you have made a firm decision, but are just exploring your opportunities and would like advice. However, I don't guarantee this is the right approach since I don't know either of you or your past correspondence. You have to judge it.