By default, state variable is attached to any model object that is passed to Machine object initalisation in transitions library. Passing model_attribute will allow us to define custom state attribute. This wasn't obvious while going through the document. TL;DR 📖🥱😜
https://github.com/pytransitions/transitions
Also django-transitions is like experimental repo and maintained since Jan 2019. So I was looking for the solution without using it. Even if we use it mentioned only about setting custom name in Mixins. Does not make sense to just to use mixins for custom variables. So example I shown in models.py is better way. Next, I need to see how I can inherit this feature into custom ModelField class.
Sample execution:
$ ./manage.py shell