Okay, so this is a bit late. I'm just adding it because it's an obvious use of the range operator for extracting the data. Using some of the tomfoolery above but trying to match the specs as I understand them (no, not trying to golf): 
use strict;
use warnings;
my $start_tag  = qr/\*\*\* begin file \*\*\*/;
my $end_tag    = qr/\*\*\* end file \*\*\*/;
my $case = '';

while ( <DATA> ) {
    # The range operator is sorely underused.
    if ( /$start_tag/ .. /$end_tag/ ) {
        if ( /$start_tag/ or /$end_tag/ ) {
            s/file/substituted file/;
        } else {
            $case = $_ & ' ' x length;
            s/old/NEW/i;
        }
        print $_ | $case;
    }
}

__DATA__
test
*** begin file ***
old_word
OLD_WORD
oLd_wOrd
olD_worD
*** end file ***
test2

[download]
Prints: 
*** begin substituted file ***
new_word
NEW_WORD
nEw_wOrd
neW_worD
*** end substituted file ***

[download]

Cheers,
Ovid

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In reply to (Ovid - coming in late) Re: Substitute Question by Ovid
in thread Substitute Question by RiotTown

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