I can answers your first question by answering your second one. If you made all the first elements of your array references Regexp objects: 
$_->[0] = qr/\b(\Q$_->[0]\E)b/ for @corrections_to_make;

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then you could do your loop as 
for my $crummy_good_ar (@corrections_to_make) {
  my ($crummy, $good) = @$crummy_good_ar;
  $file_in_string_form =~ s/$crummy/$good/ig;
}

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This way, even if you end up looping over THAT code, you'd still be dealing with already-compiled regexes. As soon as you put additional text into a regex with qr// in it: 
my $rx = qr/abc/;
if ($str =~ /^($rx)$/) { ... }

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Perl has to do the "compare physical regex forms" test. Only if the qr// object is all alone will it have the entire benefits it was made for.
Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re^5: Tokenizing and qr// <=> /g interplay by japhy
in thread Tokenizing and qr// <=> /g interplay by skyknight

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