$ perl -le'
my @numbers = ( "541321069873210200", "5413 21069873210200" );
my $start_at = 6;
my $end_digits = 4;

for ( @numbers ) {
    print;
    my @digits;
    push @digits, \substr $_, $-[0], 1 while /[0-9]/g;
    splice @digits, 0, $start_at;
    splice @digits, -$end_digits;
    $$_ = "X" for @digits;
    print;
    }
'
541321069873210200
541321XXXXXXXX0200
5413 21069873210200
5413 21XXXXXXXX0200
[download]