Patients are not limited to having 1 provider and need not worry about re establishing their provider relationships when going to a dispensary.

The only thing to remember really is that a patient and their designated provider can only have a 60 day supply in total regarding the medicine constituing that patient's 60 day supply. But dispensaries tend to not require you allow them to grow all of your or posses all of your (or any) 60 day supply so it shouldn't be a problem.