don't change lead if assigned

erpnext/crm/doctype/appointment/appointment.py

@@ -31,6 +31,7 @@ class Appointment(Document):
         if(number_of_appointments_in_same_slot >= number_of_agents):
             frappe.throw('Time slot is not available')
         # Link lead
+        if not self.lead:
             self.lead = self.find_lead_by_email()
 
     def after_insert(self):
@@ -56,6 +57,7 @@ class Appointment(Document):
                         template=template,
                         args=args,
                         subject=_('Appointment Confirmation'))
+        if frappe.session.user == "Guest":
             frappe.msgprint(
                 'Please check your email to confirm the appointment')