you have to assign the coderef to the new glob.

For simplicity the following code is a cut&paste from my scratchpad, (had to help KennethK in the CB to figure it out)

use strict;
use warnings;
$\="\n";
 
 
*tst=sub { print "orig"    };
 
tst();
 
my $safe=\&tst;
 
{
  no warnings;
  *tst=sub { print "new"};
}
 
  tst();
 
{
  no warnings;
  *tst=$safe;
}
 
  tst();
[download]

it shows how to safe, replace and reestablish a function.

If you use local *tst=sub {...} you can also restrict the new function till the end of scope.