$level1 = "LEVEL1";
$level2 = "LEVEL2";
$level3 = "LEVEL3";

$setting1 = "level1";
$setting2 = "level2";
$setting3 = "level3";

use Tie::CaseInsensitive;
tie %{$HASH{$level1}{$level2}{level3}}, 'Tie::CaseInsensitive';

$HASH{$level1}{$level2}{level3} = 3;
$HASH{$setting1}{$setting2}{setting3} = "Three";

use Data::Dumper;
print Dumper \%HASH;