I saw this Expressive C++17 challenge going around and felt like solving it in Perl 6

expressive.p6

sub MAIN($input, Str $column, Str $replacement, IO::Path $output="output.csv".IO) {
  my Str $headings = $input.IO.lines[0];
  my $index = $headings.split(",").antipairs.hash{$column};
  die "column $column not found" unless $index ~~ Int:D;
  my $fh = open $output, :w;
  LEAVE close $fh;
  for $input.IO.lines.skip: 1 -> $line {
      my @arr = $line.split(",");
      @arr[$index] = $replacement;
      $fh.say(@arr.join(","));
  }
}