I disagree with point 17.4.
I think that once a player posts picks in one tournament, he can't play in another on the same week.
It does say exactly the same in point 17.4. what you have just written in here.
You can do that only if you don't have any picks posted at the moment of the beginning of the 1st match (and further) of the tournament from which you want to withdraw.
(and further) - means you not only can't have any picks at the moment of the beginning of the first match of the tournament but in later matches as well.
It seems clear to me but if it isn't just tell me which part you don't understand.