Is there a way to disable the automatic creation of Recruiting agents' user accounts?

When we create a new recruiting agent, we would ideally like the user account that gets automatically created, to be assigned to a different User Category (RECRUITING_AGENT) that the one we use for employees (DEFAULT). Failing that, we would like to disable the automatic user account creation. Are either of these options possible?

This is because we have SSO enabled and do not need any notifications enabled for our workers however we do need notifications enabled for recruiting agents so have created a separate category. The problem is that we cannot make use of the New Account email because when the user account is created, it automatically gets assigned to the Default user category. We then have to manually assign it to the AGENT category but at that point it is too late to trigger the New Account welcome email.