First, a disclaimer: I am only speaking for my own experience, and could be totally wrong.

What I would do is use Moose's attribute extension capabilities. So, to sublclass Hubba with Bubba redefining the attribute hubba, I'd probably do:

package Bubba;
use Moose;

extends 'Hubba';

has '+hubba' => (
    is  => 'rw',
    isa => 'Str',
    builder => 'hubba_builder2',
);

sub hubba_builder2 {...}
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Of course, you'd have to know beforehand that Hubba has the attribute hubba. In my experience, this has always been the case; I always know the parent class' API before subclassing.