use Foo;
package Foo;
{
no warnings "redefine";
sub foo { 'different foo' }
}
package resume_former_namespace;
...

##</code><code>##


#!/usr/bin/perl
use warnings;
use strict;

use Foo;

use Sub::Override;

sub fixed_foo { "I'm overridden foo" }

my $override = Sub::Override->new;

$override->replace(  'Foo::foo' => \&fixed_foo );   # maybe 'foo'

print "Foo::Ridden: ", Foo::foo(), $/;

print "Foo::Ridden: ", Foo::bar, $/;

print "   ::Ridden: ", foo(), $/;
$override->restore;

print "   ::Orig: ", foo(), $/;


##</code><code>##

package Foo;
use Exporter;
our @ISA = 'Exporter';
our @EXPORT = qw/ foo bar /;

sub foo { "I'm foo" }
sub bar { foo() . 'bar' }

1;


##</code><code>##

Foo::Ridden: I'm overridden foo
Foo::Ridden: I'm overridden foobar
   ::Ridden: I'm foo
   ::Orig: I'm foo


##</code><code>##

Foo::Ridden: I'm foo
Foo::Ridden: I'm foobar
   ::Ridden: I'm overridden foo
   ::Orig: I'm foo