You should just fix the offending code. Modifying a global hash is a bad practice. If for some reason this is not possible then you can use a glob to alias the second hash temporarily.. but this is bad mojo and should be avoided. 
use strict;
use warnings;
use Data::Dumper;

use vars qw( %hash1 %hash2 );
%hash1 = (a => 1);
%hash2 = (b => 2);

do_badness();

print "hash1: ", Dumper \%hash1;
print "hash2: ", Dumper \%hash2;

sub do_badness {
    local *hash1 = \%hash2;
    bad_sub();
}

sub bad_sub {
  $hash1{c} = 3;
}

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In reply to Re: Aliasing one hash to another by imp
in thread Aliasing one hash to another by throop

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