I tried to book a partner flight via their US call center. I spoke to a surly agent that said you request your dates and they get back to you in a month, maybe longer (I swear the agent said this). I said what if no flights are available on the dates I choose? The unfriendly agent responded "too bad, you can start the process again." At that point I gave up and decided to use my points on EK via the web. I too am still waiting for a definitive answer on date changes.