I posted about this a few years ago but this problem remains unfixed.
 
I regularly make large "Blurb Photo Book"s in the LR Book Module that bump up against the 440 page limit using standard paper.  I also have really lousy internet.  I sometimes have to print a "PDF" book to a thumbdrive to upload at a different location with faster internet.  This works well.
 
The problem occurs when I want to switch back to a "Blurb Photo Book" from "PDF" in the Book Module.  I get the following error message:

Clearly this is a serious problem for me and one I dont dare try to experiment with to work around.  I believe it would not be difficult to set the Blurb Photo Book paper to "standard" paper to avoid this problem.