Is there a way, in Django, to define routes using Flask-style route syntax?
Have not personally used it, but this sounds exactly what you are asking about - django-fsu:
Flask-Style URL Patterns for Django
I would though still try to stick to Django URL-routing style and avoid "transitional" solutions like this. You can also use django-fsu temporarily to migrate, then cover all the endpoints with end-to-end and functional tests and, then, once you have the coverage, migrate to the Django native URL routing style.