use Module;  # Execute module first so it doesn't replace you!

BEGIN {
   package Module;
   no warnings 'override';
   sub func {
      ...
   }
}

##</code><code>##

use Module;  # Execute module first so it doesn't replace you!

BEGIN {
   package Module;
   no warnings 'override';
   *func = sub {
      ...
   };
}

##</code><code>##

use Module;  # Execute module first so it doesn't replace you!

BEGIN {
   package Module;
   no warnings 'override';
   my $orig_func = \&func;
   sub func {
      ...
      $orig_func->(...)
      ...
   };
}

##</code><code>##

use Module;  # Execute module first so it doesn't replace you!

{
   package Module;
   no warnings 'override';
   my $orig_func = \&func;
   local *func = sub {
      ...
      $orig_func->(...)
      ...
   };
   # Replaced from here.
   ...
   # Replaced until here.
}

##</code><code>##

>perl -c -we"sub foo { my $x; sub bar { $x } }"
Variable "$x" will not stay shared at -e line 1.
-e syntax OK