FYI: I just got my multiple entry visa aproved and i provided only a flight to Thailand and a flight out of Thailand. The only thing that sucks is that the visa is valid 6 months from today and not from the end of october when i'm actualy leaving.
I talked to the embasy now and they told me that if i exstend a multiple entry TR visa then the extension is counted as a different visa. Since you only allowed to hold one visa at the time the TR visa will be invalid after extension.
Furthermore the ambassador recommended me to get a single entry visa and told me if i ask the immigration office nicly to extend it for more than 30 days they might be able to sort me out...