Can I tactfully change my mind after agreeing to do an independent study with a professor?
Do you have a project already lined up ? it sounds like your meeting with the first professor would be to discuss topics for the study. In any case, if no financial agreement has been reached, I see no harm in talking with both professors and then making a decision based on what happens in those meetings. I disagree with @aeismail that you've given a formal commitment at this stage. 

You didn't say though why you'd prefer to work with the second professor prior to having a meeting ? is it the subject matter ? general rapport ?