in reply to A novice's thoughts on applying Demeter to extension code

Update: Of course, it would help if I actually remembered that sub PACKAGE::name {} is legal syntax. *sighs* It's Monday.

What about plugging in your new logic into the original namespace? 

package Employee::MyStuff;

package Employee;

sub ManagersCostCenter {
    my $self = shift;
    $self->Manager->CostCenter;
}

1;
__END__

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Put that into Employee/MyStuff.pm and you're good to go.

Of course, you're now fiddling with the internals of a class you don't control, which means that you're violating encapsulation. You also, everywhere you use Employee, have to now do: 

use Employee;
use Employee::MyStuff;

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In that order would be preferable (though not absolutely required).

This is a somewhat common thing to do on CPAN. (q.v. URI and URI::QueryParam for a good example of this)

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

In Section Meditations