Yes, Referring Physician can be changed in SOAP notes.
Start by entering a Referral doctor in patient information.
Navigate to > Manage Patients > Patient Information.
Select Referral doctor from autofill drop-down and then click "Save & Continue".
When a new note is created the Referral physician will be picked from patient information.
Anytime a user can change the Referring Physician in an existing SOAP note provided the note is not completed.
The above steps are applicable to all the SOAP notes.