It's also possible to change route by eternal post.
@skarlath:
No. They jumped route when they went to Alabastsa, because that required an Eternal Compass. Skypiea was the next on the Log Pose, however, whatever Island they were supposed to go to after is up for discussion.
So the original break was to Alabasta, then they possibly broke this new path once they came down from Skypiea
Skypiea is NOT the next island after Alabasta. After Alabasta is some kind of autumn island somewhere we never got to see (most likely not Jaya as Nami would have known that). The logpose drastically changed direction after the ship fell from the sky. So it is possible that a logpose can change mid travel locking on to another magnetic field, it just seems to be very rare.
And they didn't break from skypiea > longringlong island > Water 7 > FI. The log pointed to longringlong and they have followed it without it resetting on some island belonging to another path since.