gistfile1.py

class MyCustomModelChoiceField(ModelChoiceField):
    def label_from_instance(self, obj):
        mapping = {
          "A1": "B1",
          "A2": "B2",
          # ... etc
        }
        if obj.name in mapping.keys():
            return "New type - %s" % (mapping[obj.name])
        else:
            # default back to original functionality
            return smart_unicode(obj)