I would think not. I recently flew a multi-city itinerary on UA with 3 days between each leg. 1st leg I put in my TK number, then 2 days later when I checked in for my next leg I changed it back to my UA number and on the 3rd day the first two flights I had taken posted to my MP account since that was the number on the reservation when they posted.

You could fly the flights without a FF number in the reservation and request retroactive credit later. I'm not sure how easy that is to do with A3 though.