my $h = {k1 => { k2 => { k3 => 'wert' }}};
@keys = qw(k1 k2 k3);
$hxx = $h;
$hxx = $hxx->{$_} for @keys[0..$#keys-1];
$hxx->{$keys[-1]} = 'neuerWert';
use Data::Dumper;
print Dumper $h;