Mystery Permission Sets assigned to Guest Users

Permission Set Assignments are data in the org. The DML operation cannot be performed by a Change Set - but this sample code might help you in automating the assignments.

// the user reference
User u = new User();

// the names of the permission sets you need to assign
List<String> permissionSets = new List<String>{'permission_set_name_1','permission_set_name_2'};

// the assignment records for DML
List<PermissionSetAssignment> psAssignments = new List<PermissionSetAssignment>();

// query for the sets and assign to the user
for (PermissionSet ps : [SELECT Id, Name
                           FROM PermissionSet
                          WHERE Name IN :permissionSets]) {
    psAssignments.add(
        new PermissionSetAssignment(
            AssigneeId      = u.Id,
            PermissionSetId = ps.Id
        )
    );
}

// insert the assignments
insert psAssignments;