#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'key1' => 'test1',
	     'key2' => 'test2',
	     'key3' => 'test2',
    );

print Dumper \%hash;

$hash{'key4'} = delete $hash{'key1'};

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          'key1' => 'test1',
          'key3' => 'test2',
          'key2' => 'test2'
        };
$VAR1 = {
          'key2' => 'test2',
          'key3' => 'test2',
          'key4' => 'test1'
        };

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'key1' => 'test1',
	     'key2' => 'test2',
	     'key3' => 'test2',
	     'key4' => 'test4',
    );

print Dumper \%hash;

my @oldKeys = sort keys %hash;
print Dumper \@oldKeys;

# Remove what ever keys you want to keep e.g. key1 key3
splice @oldKeys, 0, 1;
splice @oldKeys, 1, 1;

print Dumper \@oldKeys;

my @newKeys = ('key5', 'key6');
@hash{@newKeys} = delete @hash{@oldKeys};

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          'key2' => 'test2',
          'key3' => 'test2',
          'key1' => 'test1',
          'key4' => 'test4'
        };
$VAR1 = [
          'key1',
          'key2',
          'key3',
          'key4'
        ];
$VAR1 = [
          'key2',
          'key4'
        ];
$VAR1 = {
          'key6' => 'test4',
          'key5' => 'test2',
          'key1' => 'test1',
          'key3' => 'test2'
        };

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'key1' => 'test1',
	     'key2' => 'test2',
	     'key3' => 'test3',
    );

print Dumper \%hash;

my @new_keys = keys %hash;
y/key[0-9]/alt[0-9]/ for @new_keys;
@hash{@new_keys} = delete @hash{keys %hash};

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          'key1' => 'test1',
          'key2' => 'test2',
          'key3' => 'test3'
        };
$VAR1 = {
          'alt3' => 'test3',
          'alt2' => 'test2',
          'alt1' => 'test1'
        };

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'key1' => 'test1',
	     'key2' => 'test2',
	     'key3' => 'test3',
    );

print Dumper \%hash;

%hash = map { y/key[0-9]/alt[0-9]/r => $hash{$_} } keys(%hash);

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          'key2' => 'test2',
          'key1' => 'test1',
          'key3' => 'test3'
        };
$VAR1 = {
          'alt3' => 'test3',
          'alt2' => 'test2',
          'alt1' => 'test1'
        };