sub dive_val :lvalue {
   my $p = \shift;
   $p = \( $$p->{$_} ) for @_;
   $$p
}

my @paths = ('key1', 'key2:key22', 'key2:key23');

for my $path (@paths) {
   my @path = split(/:/, $path);
   my $new_val = ...;
   dive_val(\%hash, @path) = $new_val;
}