I don't think BMW changed anything about the actual alarm. They changed it from a dealer option to a factory option. I don't think there will be an OEM option after the car is built. I found out about the change two days before my car went into production and was able to get the change made.
Maybe you can talk with your dealership and have them install the OEM alarm for the $400 that it would have been as an option. It will be a more complicated installation but it seems most dealers did not know about the change or at least did not notify their customers.