To get an RTR ( A ) you have to give both part1 and part 2 in the same attempt
So yes you will have to give part 1 again
And no none of the airlines want an RTR ( A ) . All they want is just a valid RT license . The privileges of an RTR A , P , C are the same .
The reason they post RTR(A) in the requirements is because their HR department that gives the info on the website is not aware of the different classes of RTR available .
Getting an RTR ( A) is beneficial in the long run as you can obtain one with lifetime validity . That way you will never have to bother about dealing with the WPC ever again ( unless your RT is lost and you have to obtain a new one )