I'd use more complex data structures which would make it more extensible.

#!/usr/bin/perl -w

use strict;
use Data::Dumper;

my @Def = ( { name => 'Group1',
          code => [qw( H0 K0 PA PB PC PD PE PF PG PH )] },
        { name => 'Group2',
          code => [qw( PX PY PZ P1 P2 P3 P4 P5 P6 P7 )] });

my %Codes;

foreach (@Def) {
  @Codes{@{$_->{code}}} = ($_->{name}) x @{$_->{code}};
}

my %Groups;
while (<STDIN>) {
  chomp;
  push @{$Groups{$Codes{substr($_, 0, 2)}}}, $_;
}

print Dumper \%Groups;
[download]

You end up with the partitioned data in %Groups. I tested it with this input file:

K0blah
PZfoo
P7bar
PEbaz
[download]

which gave the following output:

$VAR1 = {
          'Group1' => [
                        'K0blah',
                        'PEbaz'
                      ],
          'Group2' => [
                        'PZfoo',
                        'P7bar'
                      ]
        };
[download]

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg