It's trivial using the mighty MCE::Shared by marioroy, two extra lines:

package MyClass {
    use Moose;
    has foo => ( is => 'rw', default => 'bar' ); 
};

package main {
    use strict; use warnings; use feature 'say';
    use MCE::Shared;

    my $obj = MCE::Shared->share({ module => 'MyClass' });

    say 'Before forking: ' . $obj->foo;

    my $pid = fork;

    if ( $pid == 0 ) {
        $obj->foo('baz');
        exit;
    } else {
        waitpid $pid, 0;
    }

    say 'After forking: ' . $obj->foo;
};
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Output:

$ perl 1210687.pl

Before forking: bar
After forking: baz
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For details see the documentation on sharing objects between processes with MCE::Shared.

Hope this helps!