package boo;

sub to_s { "a boo" };

package bar;

sub to_s { "a bar" };

package main;

sub doit {
  my $boo = shift;

  my $reblesser = Reblesser->new;

  $reblesser->rebless($boo, "bar"); 
  print "within: ", $boo->to_s, "\n"; # "a bar"

  # here the scope of the reblesser ends and so the reblessing it did
}

my $obj = bless {}, 'boo';
print "before: ", $obj->to_s, "\n"; # "a boo"
doit($obj);
print "after: ", $obj->to_s, "\n"; # "a boo" again