use Data::Dumper;
sub set : lvalue {
  @_ == 1 ? $_[0] : set($_[0]{$_[1]},@_[2..$#_]);
}

my $h = {foo => 1,
         bar => 2,
         baz => {
                 troz => 3,
                 zort => 4,
                 poit => {
                          qux  => 5,
                          quux => 6,
                         },
                },
        };

print Dumper($h);
set($h, qw/baz troz/) = 42;
set($h, qw/baz poit qux/) = 17;
print Dumper($h);