$tmp=(get the file contents);
$tmp=~s/\r//g;
$tmp="\n$tmp\n";

($n,$v)=[got from somewhere, same as list items]
($ctr)=[got from somewhere else]
($rctr)=[count of replacements made]

## attempt 1

if ($tmp=~/^$n\t$v$/) {          
   $tmp=~s/^$n\t$v$/$n\t$v\t$ctr/;
   $rctr++;
} else {

....