use strict;
use Example::Module;

# add a new sub to the package
sub Example::Module::bar {
  my ($s, $v1, $v2) = @_;
  print "Bye '$v1' and '$v2'\n";
}

my $em = Example::Module->new;
$em->bar("one", "two");

# call the sub not as a method
Example::Module::foo('one', 'two', 'three');

# change the existing sub
*Example::Module::foo = sub {
  my ($s, $v1, $v2) = @_;
  print "Oops '$v1' and '$v2'\n";
};

$em->foo("one", "two");