I don't think that's a question he can answer quickly. If it involves changing the SKUs that are already up for preorder and people have paid for then it's a question that will involve a lot of the management of the company I would assume. At this point the best option might be to have a stock of heads that can be bought as expansion packs to complement the figure that we have already ordered.
This would probably be the easiest way to offer both options without affecting existing pre-orders. I really hope Asmus considers this as an option. If offering both heads individually is not an option, then maybe offer just one separately. Then those of us who would like both can pre-order the individual head sculpt and the full figure with the other head sculpt.