Would this help?

use strict;
use warnings;

open OUTPUT, '>', 'output.txt' or die;

my @record;
my $uid_flag = 0;

while (<DATA>){
  chomp;
  unless ( /^$/ ){
    push @record, $_;
    $uid_flag++ if /^uid/;
  }
  else{
    for ( @record ){
      print OUTPUT "$_\n";
        if ( /^cn/ and ! $uid_flag ){
          my ( $field, $value ) = split ':';
          print OUTPUT "uid:$value\n";
        }
    }
    @record = ();
    $uid_flag = 0;
    print OUTPUT "\n";
  }
}
close OUTPUT;

__DATA__
dn: cn=MTOP,cn=users,dc=myco,dc=com
orcldefaultprofilegroup: cn=myco,cn=portal_groups,cn=groups,dc=myco,dc
+=com
cn: MTOP
orclactivestartdate: 20031028060637Z
objectclass: top
objectclass: person
objectclass: inetOrgPerson
objectclass: organizationalPerson
objectclass: orclUser
objectclass: orclUserV2
sn: Joe
givenname: Blow
o: myo
userpassword: {MD4}oLezu+AceuHBDEBHFuVDwg==

dn: cn=me,cn=users,dc=polk,dc=com
orcldefaultprofilegroup: cn=user_grp,cn=portal_groups,cn=groups,dc=myc
+o,dc=com
userpassword: {MD4}oLezu+AceuHBDEBHFuVDwg==
orclactivestartdate: 20031030114555Z
objectclass: top
objectclass: person
objectclass: inetOrgPerson
objectclass: organizationalPerson
objectclass: orclUser
objectclass: orclUserV2
cn: me
uid: me
sn: Administrator
givenname: me
o: myco
[download]

Produces...

dn: cn=MTOP,cn=users,dc=myco,dc=com
orcldefaultprofilegroup: cn=myco,cn=portal_groups,cn=groups,dc=myco,dc
+=com
cn: MTOP
uid: MTOP
orclactivestartdate: 20031028060637Z
objectclass: top
objectclass: person
objectclass: inetOrgPerson
objectclass: organizationalPerson
objectclass: orclUser
objectclass: orclUserV2
sn: Joe
givenname: Blow
o: myo
userpassword: {MD4}oLezu+AceuHBDEBHFuVDwg==

dn: cn=me,cn=users,dc=polk,dc=com
orcldefaultprofilegroup: cn=user_grp,cn=portal_groups,cn=groups,dc=myc
+o,dc=com
userpassword: {MD4}oLezu+AceuHBDEBHFuVDwg==
orclactivestartdate: 20031030114555Z
objectclass: top
objectclass: person
objectclass: inetOrgPerson
objectclass: organizationalPerson
objectclass: orclUser
objectclass: orclUserV2
cn: me
uid: me
sn: Administrator
givenname: me
o: myco
[download]

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