Can a driver alternate between the two 150 air-mile exceptions?

Yes. If during a seven-day period a driver operates some days under the exception in 395.1(e)(1), some days under the non-CDL exception in 395.1(e)(2), and some days under neither, the driver must comply with the provisions of whichever exception applies for the entire duty period (usually one day). The driver must remain under the conditions of the exception for the entire duty period, but compliance may vary from one duty period to the next, depending on operating circumstances.