Yes, you can change the object to which a thingy is tied in one of the objects accessor methods (FETCH, STORE, etc), provided you write directly to $_[0].

For example, suppose you want to wrap Apache::Session, so that on first store or fetch, it does some init before becoming a real session object...

package My::Apache::Session;
sub TIEHASH {
  my $class = shift;
  bless [@_], $class; # remember real args
}
sub FETCH {
  ## DO NOT USE shift HERE
  $_[0]->my_initialization;
  $_[0] = Apache::Session->TIEHASH(@{$_[0]});
  goto &{$_[0]->can("FETCH")};
}
sub STORE {
  ## DO NOT USE shift HERE
  $_[0]->my_initialization;
  $_[0] = Apache::Session->TIEHASH(@{$_[0]});
  goto &{$_[0]->can("STORE")};
}
sub my_initialization { ... }

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