If I post a WL book fifo, and the book is offered to someone that I don't want to send to (prior issue) how do you decline that but be able to send to someone else? Thanks...

After they accept it you would need to cancel the transaction. They'll be #1 in the WL though so you'll probably need to wait to repost it. I guess you could WL it yourself, going to the end of the line so you could see the info on how the WL line is moving.  Then remove yourself once you see it's gone on to the next member or so and you can 'safely' repost.