That's half the battle. You will actually have to fly them

And are you sure that booking them now is within the terms of the offer?

I know I am being possibly over-pedantic here, but the English text could be interpreted that they must also be booked during the stated period:

The new edition of the MilleMiglia Program will also include a special initiative for our most loyal members: purchase and take at least 4 one way flights between 1 January and 31 March 2018 and carry over into the new edition up to 100% of the remaining miles at 1 April 2018.

(I am waiting for further news of the changes to determine whether to just burn the miles I have left, rather than attempting to "save" them with a booking next year if the long-term future of the programme looks bright)