If you need to customize any serializer behaviour you can use the DJOSER['SERIALIZERS'] setting to use your own serializer classes in the built-in views. Or if you need to completely change the default djoser behaviour, you can always override djoser views with your own custom ones.

Define custom urls instead of reusing djoser.urls:

urlpatterns = patterns('',
    url(r'^register/$', views.CustomRegistrationView.as_view()),

Define custom view/serializer (inherit from one of djoser class) and override necessary method/field:

class CustomRegistrationView(djoser.views.RegistrationView):

    def send_activation_email(self, *args, **kwargs):
        your_custom_email_sender(*args, **kwargs)

You could check djoser API in source code: