I've done more than 4 legs on a one-way several times. I did REP-KUL-TPE-KIX-NRT-LAX and also LAX-YVR-JFK-AUH-DOH-MAA. Both were allowed. I booked more direct segments and the called in to change one segment into two a few different times. I don't know that there is any way to know for sure if it's allowed until you call in and try. If it doesn't work the first time HUCA.