Hi CruiseDad, yes you can download them as many times as you want it seems. You don't need to notify Carnival. I am pretty sure that once you view the Docs it will cancel the "Blue Book" regardless if you download the file or not. We got our mailed Docs with a postmark date of 33 days prior to sailing. So I am guessing to add a week to that to avoid getting the mailed Docs as they may be in que by then to be printed and mailed.
If you don't mind me asking, why don't you want the "Blue Book" ?