(I guess what I'm really asking is - is there a way to change the class of an object that already exists under Moose? Or perhaps this is not the done thing?)

Pretty much the same sort of question I asked a while ago here. The quick answer is as follows:

package Dog;
use Moose;
has 'breed' => ( is => 'ro',isa=>'String');
has 'color' => ( is => 'rw', isa=>'String');

sub BUILD { 
     my $self =shift;
     my $class = "Dog::" . $self->breed();

     $class->meta->rebless_instance($self);

} 
1;
[download]

and somewhere in user space:

| handwaving here..
use Dog;

    # updated this on 2013-04-24, error in original code
    my $dog = Dog->new(breed=>'Poodle');
|
|
[download]