You may have the impression that if you claim something about your interest, they will force you to do work on it during your program. Although, it is always good to be honest and straightforward. But sometimes you are not really sure what you want to do for your PhD, then do not be afraid. If you take up something in the beginning, there is always a chance to later switch to other subjects in the same department. Also, people do not look at your personal statement every day to see what you have claimed when you were applying.
If you are highly interested to get into a specific university, it is a good idea to prepare a separate Personal Statement for them and describe why you are interested to get into their program and how your skills and experiences are appropriate for that department.