I think you should, although I haven't actually looked at the official policy. When I booked my flights, EMSpace was a ripoff, so I decided not to get it, and paid for EMSpeed instead. I changed my mind later (I have a tight connection), and asked how much EMSpace was (I booked with points so I am unable to touch the itinerary online) and was told less than half of what the website quoted me, so I called in to add it. They said that the procedure would be to refund me the EMSpeed fee, and charge me the EMSpace fee.