...
my $echo = 'ECHO';
my ($dffname, $listname) = @ARGV;
my $fh;

# read key/val lists
open $fh, '<', $dffname or die "$dffname $!";
my %lijst = map { chomp; (split /\t|\s{2,}/)[1,0] } <$fh>;
close $fh;

# readfile list
open $fh, '<', $listname or die "$listname $!";
my @listfiles = <$fh>; chomp @listfiles;
close $fh;

for my $file (@listfiles) {
   # read original file
   open $fh, '<', $file or die "$file $!";
   local $/;  my $content = <$fh>;
   close $fh;

   # modify content
   while( my ($key, $val) = each %lijst ) {
      next unless $val == 1;
      $content =~ s/^$key$/$echo/gms;
      $content =~ s/^$key$/$echo/;   # re-subsitute first (?)
   }
   # write modified file
   open $fh, '>', "$file.out" or die "$file.out $!";
   print $fh $content
}
...