"...preserve values..."

Mmh, i'm not sure if this is helpful but a while ago i played around with this:

package Foo {

    use strict;
    use warnings;

    sub new {
        my ( $class, $foo ) = @_;
        bless \$foo, $class;
        \$foo;
    }

    sub foo {
        ${ (shift) };
    }

    1;
}

package Bar {

    use strict;
    use warnings;
    use parent qw(Foo);

    my $modify = sub { uc shift };

    # my $modify = sub { ... };

    sub bar {
        # my ( $self, $foo ) = @_;
        $modify->( shift->SUPER::foo() );
    }

    1;
}

#!/usr/bin/env perl

use strict;
use warnings;
use feature qw(say);
use Bar;

my $object = Bar->new(q(lorem ipsum kizuaheli));

say for ( $object->foo(), $object->bar() );

__END__
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OK, it's a scalar but it could hash as well. The original is always available.

I hope i didn't miss the point.

Regards, Karl