This seems to handle the pathological cases?

#! perl -lsw
use strict;

my @reps = map{ sprintf '%05d', $_ } 0 .. 20;
while(<DATA>) {
    my $n=0;
       # redundant /e option  removed 
       # per [Abigail-II]'s comment below.
    s/\d{5}/$reps[$n++]/g;   
    print;
}
__DATA__
0000000000000000000000000000000000000000000000000000000000000000000000
+0000000000000000
00000xxxx00000xxxxx00000xxxx00000xxxxx00000xxx00000xxx00000xx00000xxx0
+0000x00000x00000
[download]

Outputs

c:\test>234342
0000000001000020000300004000050000600007000080000900010000110001200013
+0001400015000160

00000xxxx00001xxxxx00002xxxx00003xxxxx00004xxx00005xxx00006xx00007xxx0
+0008x00009x00010
[download]