Using 2 times the 144 h visa within 2 weeks

Hi,
is it possible to fly Bangkok - Beijing, stay for maybe 2 nights (first 144 h free transit, but just use 2 or 3 days). Then
fly to Tokio for 2 or 3 nights and return to Beijing and get a second 144h free transit?

2. question: Do you really need confirmed seats to get the visa? Because with some airlines you are only able to chose them within the online check in process.