I played around with perl and this should give you a randomized sequence each time:

#!/usr/bin/perl
use strict;
use warnings;
my $num_args = $#ARGV + 1;
if ($num_args != 2) {
    print "\nUsage: aminoRand.pl <Codon Table File> <nucleotide sequence>\n";
    exit;
}

open CODON, $ARGV[0] or die $!;

my %codon = ();
my %translate = ();
while (<CODON>) {
  chomp;
  if ( /^\s*$/ ) { 
  }else{
      my @list = split( /\s+/, $_);
      my $key = $list[0];
      my @codes = @list;
      @codes = splice @codes, 1, @codes;
      $codon{$key} = \@codes;
      for(my $i = 1; $i < $#list+1; ++$i){
        $translate{$list[$i]} = $key;
      }
  }
}
close(CODON);
chomp($ARGV[1]);
my $length = length($ARGV[1]);
for(my $i = 0; $i < $length; $i=$i+3){
    my $current = substr $ARGV[1], $i, 3;
    if(exists $translate{$current}){
        my $newKey=$translate{$current};
        if(exists $codon{$newKey}){
        my @possible = @{$codon{$newKey}};
        print($possible[rand @possible]);
        }
        else{
            print "Cannot find in codon: $newKey\n";
        }
    }
    else{
        print "Can't find: $current\n";
    }
}
print("\n");

You will need to provide a codon file of the following format:

I  ATT  ATC  ATA
L  CTT  CTC  CTA  CTG  TTA  TTG

and then the sequence. Then it will randomly generate a sequence that will produce the same amino acid sequence but different neucleotide