foreach $replace (@substitutionlist) {

     ($oldline, $newline) = split(/\t/, $replace);
     $newline = s/\s/_SPACE_/g;
    #….more code here

     foreach $line (@array) {
          $count += s/\b$oldline\b/$spliced/eg for @array;
          #….more code here
     }
}
s/_SPACE_/ /g for @array;