Assuming you don't have any multi-valued CGI parameters, I'd probably do something like this:

#!/usr/bin/perl -w
use strict;

use CGI qw(param url);

my $me = url;

my %params;
my @params = param;

$params{$_} = param($_) foreach @params;

my @value = qw(AAA BBB CCC DDD);

foreach my $v (@value) {
  foreach my $p (0 .. $#params) {
    print "$me?".
           join '&',
                 map { "$params[$_]=" . 
                       ($p == $_ ? $v : $params{$params[$_]}) }
                      0 .. $#params;
    print "\n";
  }
  print "\n";
}
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"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg

#!/usr/bin/perl

use URI;

my $ORIG = "http://myurl.com/page.pl?key1=va1&key2=val2&key3=val3";

my @value = qw(AAA BBB CCC DDD);

my $u = URI->new($ORIG);
my %params =  $u->query_form;

for my $newvalue (@value) {
  for my $key (sort keys %params) {
    my %p = (%params, $key, $newvalue);
    $u->query_form(%p);
    print "$u\n";
  }
}
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-- Randal L. Schwartz, Perl hacker

$url='http://myurl.com/page.pl?key1=val1&key2=val2&key3=val3';
@value = ("AAA", "BBB", "CCC", "DDD");
for $val (@value)    {
    for (1..3)    {
        $t=$url;
        $t=~s/\bkey$_=val$_\b/key$_=$val/i;
        print $t,$/;
    }
}
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$_=$,=q,\,@4O,,s,^$,$\,,s,s,^,b9,s,
$_^=q,$\^-]!,,print
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