#!/usr/bin/env perl

use strict;
use warnings;

use Data::Dump;

my %hash = (
    xxx_text10_yyy => 1,
    xxx_text11_yyy => 1,
    mmm_text12_nnn => 1,
    mmm_text13_nnn => 1,
    abc_text6_ghi  => 1,
    abc_text7_ghi  => 1,
    abc_text8_ghi  => 1,
    abc_text9_ghi  => 1
);  

my %xref = (
    abc => 'boom',
    mmm => 'doom',
    xxx => 'zoom',
);

my $re = qr{(?x: ^ ( [^_]+ ) _ ( [^_]+ ) )};

/$re/ and $hash{$_} = join '_', $xref{$1}, $2 for keys %hash;

dd \%hash;