There may be a better way, but you can do this by overriding new (and removing the title attribute from Employee::Former):

class Employee::Former is Employee {
    method new(*%params) {
        %params<title> //= 'Team Member';
        return callwith(|%params);
    }

    method name_and_title {
        my $old = callsame;
        return "$old (Former)";
    }
}
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