Hi @KIP
Welcome to the Auth0 Community!
Thank you for posting your questions; due to the event object nature, it’s currently not possible to achieve a scenario where assigning users to a role and adding them to the custom claims in the token will be split into two actions. Right now, the best option is to merge them into a single action. However, I encourage you to raise this question as a product feature request in the Feedback category. You can read our FAQ regarding submitting a feature request here: How to Submit Product Feedback or Feature Requests
Thanks
Dawid