A general solution: 
my $nth = 4;
my $str = 'a=>bb=>ccc=>dddd=>eeeee=>ffffff';

while ($str =~ /=>/g) {
    if (--$nth == 0) {
        substr($str, $-[0], $+[0] - $-[0], '~~|~~');
        last;
    }
}
print "$str\n";

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In reply to Re: Replace the nth occurence by trizen
in thread Replace the nth occurence by Anonymous Monk

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