use strict;
use warnings;

while(<DATA>) {
    my ($colA, $colB, $colC,$colD) = unpack "A19A15A7A45";
    $colC = "N/A" if $colC eq "XYZ" and $colD =~ /Region/;
    print "$colA -- $colB -- $colC -- $colD\n";
}

__DATA__
ValuesInColumn1    DataColumnB    XYZ    RowDescription|RowCode|Supplier ID::Region
ValuesInColumn1    DataColumnB    XYZ    RowDescription|RowCode|Supplier ID::Region
ValuesInColumn1    DataColumnB    XYZ    RowDescription|RowCode|Supplier ID::Region
ValuesInColumn1    DataColumnB    XYZ    RowDescription at RowCode
ValuesInColumn1    DataColumnB    ABC    RowDescription at RowCode