How to choose a connect a user category while creating a Non-worker person record

We are implementing a new person type called as Non-worker, we are able to create the employment record but we want to associate this person type with a new user category in security console where the username will be their email address. For all Emp/CWK the username is defined by "Default" User category where person number is the username but for Non-workers we want to handle them differently. With creating user account with HDL we can pass the user category but when a Manager is hiring/creating a new Non-worker then how will that specific user category be chosen at that