@lambert-torres
Hiya,
There is no way to update a user Id after the account has been created. However, you can always specify a valid UUID when creating a user (and, indeed, most other FusionAuth resources).
Simply provide a valid UUID on the path of the POST request.
https://fusionauth.io/docs/v1/tech/apis/users#create-a-user has more.
Based on what you shared, that should work. Let me know if there's nuance I missed.
Thanks for using FusionAuth!
Dan