$_->[0] = qr/\b(\Q$_->[0]\E)b/ for @corrections_to_make;

##</code><code>##

for my $crummy_good_ar (@corrections_to_make) {
  my ($crummy, $good) = @$crummy_good_ar;
  $file_in_string_form =~ s/$crummy/$good/ig;
}

##</code><code>##

my $rx = qr/abc/;
if ($str =~ /^($rx)$/) { ... }