If you really want to redefine methods on a per-object basis, one way to do it is to construct a new class for each object which inherrits from your base class. For example:

package shortTest;
use strict;
1;

sub new {
  my $class = shift;
  my ( $name ) = @_;

  my $self  = {};
  my $new_class = $class . '::' . $self;

  {  
      no strict 'refs';
      @{ $new_class . '::' . 'ISA' } = ( $class );
      *{ $new_class . '::' . 'getName' } = \&showName;
  }
  bless $self, $new_class;

  $self->{name} = $name;

  return $self;
}

sub updateName {
  my $self = shift;
  my $class = ref $self;
  no strict 'refs';
  *{ $class . '::' . 'getName' } = \&showName2;
}
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Update: Added no strict 'refs'