#!/usr/bin/perl -w
use strict;
use Smart::Comments;
my $string = '423RY75Y69827EC67592C78657N965R345U299M';
my $correct = '423R_Y75Y_69827E_C67592C_78657N965R_345U_299M';
$string=~s/([A-MO-Za-mo-z])([\dN]+)\1/_$1$2$1_/g;

### $string
# is now '423R_Y75Y_69827E_C67592C_78657N965R345U299M'

# now i have troubles..
# the idea is to match right to left, and if after (the last digit
# or N char), place an underscore, unless of course, that char is the 
# char we started with!
$string=~s/([^\dN\3])([\dN]+)([A-MO-Za-mo-z])/$1_$2$3/g;

### $string

# is now '423R_Y_75Y__69827E_C_67592C__78657N965R345U_299M'
# wow, seems to have done the reverse of what i wanted!