Hmmm... don't know if this is the best solution (nor if it's really what you meant to do), but this might be what you need:

use strict;
my (@newarray,@array1,@array2);
#Fill @array1 and @array2 with hashrefs here...
my $count = 0;
foreach my $element1 (@array1) {
   foreach my $element2 (@array2) {
      foreach my $key (keys %{$element1}) {
         next if (%{$element1}->{$key} == %{$element2}->{$key});
         %{$newarray[$count]} = %{$element1};
         my $val = $newarray[$count]->{$key};
         delete $newarray[$count]->{$key};
         %{$newarray[$count]}->{'CHANGED'} = $val;
      }
   }
}
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