Following up on the remark to look up unicode support in Perl, you'll need to know the name of the character encoding used in your data. IIRC, "Traditional Chinese" would refer to some sort of "Big5" encoding, but there might be more than one sort of "Big5", and the difference might matter. (My Perl 5.8.1 on macosx/panther supports "big5-eten" and and "big5-hkscs"; there might also be a "CP???" version.)

Whatever character set is appropriate, it might be easiest to save a plain text file containing just the "CHT string" (or both the preceding and the following "CHT string", if these are not identical), in the same character set as the original data. Then something like this should do:

use strict;
use Encode;

open( I, "string.txt" );
my $string = <I>;
chomp $string;   # or: my ($pre,$fol) = split ' ',$string;
                 # if file has previous and following strings
close I;

my $pattern = decode( 'big5-eten', $string );

# you might need a different character-set name (if so, fix it in thre
+e places)
# also, if you are using $pre and $fol, you need to decode each one se
+parately
# (e.g. into $pat1 and $pat2)

my $newversion = "2.0";  # or whatever...

open( I, "<:encoding(big5-eten)", "big_data.txt" );

binmode( STDOUT, ":encoding(big5-eten" );

while ( <I> )
{
    s/($pattern).*?($pattern)/$1$newversion$2/;
# or:  s/($pat1).*?($pat2)/$1$newversion$2/;
# maybe you also need the "g" modifier too?

    print;
}
[download]

(not tested, of course, but nothing much to it, really)