I am scheduled to fly Turkish Airline on an international trip (around 18k miles for the round trip). On the way there, I am booked into class P. On the way back, I am booked into class S. According to United's website, I will earn 100% miles for class S and nothing in class P.

Do I need to use the same Frequent flyer # for the entire trip? Could I enter my Turkish frequent flyer # originally to earn Turkish miles for the outbound flight, and then change to my United # for the inbound flight? Would that be allowed? '

Many thanks!