use v5.12.0;
use warnings;


# ========= mock original module
BEGIN {
    package zor;

    my $varry = "DEFAULT";

    sub lol {
        $varry = 'OLD';
        return 'whatever';
    }

    sub get_varry {
        return $varry
    }

    # ========= old behaviour
    warn get_varry;
    warn lol();
    warn get_varry;

}

package main;




# ========= monkey patch sub
{
    package zor;

    use PadWalker qw/closed_over/;
    my ($h_closure,$s_varry);


    # ===== get scalar ref of varry
    BEGIN {
        $h_closure = closed_over(\&lol);
        $s_varry = $h_closure->{'$varry'};
    }

    # ===== new sub
    no warnings 'redefine';
    sub lol {
        $$s_varry = 'NEW';
        return 'whatever';
    }
}


# ========= new behaviour
warn zor::lol();
warn zor::get_varry;                    # OOPS


##</code><code>##

DEFAULT at d:/Perl/pm/change_my.pl line 21.
whatever at d:/Perl/pm/change_my.pl line 22.
OLD at d:/Perl/pm/change_my.pl line 23.
whatever at d:/Perl/pm/change_my.pl line 54.
NEW at d:/Perl/pm/change_my.pl line 55.