I saw someone suggest adding a lot of tylose to the fondant to get it to set up for the edges of the book.. All I could find was gumpaste mix.. can I work that into my fondant to make it more firm??

If so.. what stage would I add that to a mmf recipe?

Thank you in advance!

Gumtex is essentially the same thing as tylose (I cannot get tylose either). A lot would give it a really lousy taste and if you want people to eat it and like it....
I am not sure what you mean by set up, as I have never made a book cake. But for my photo album I just used fondant. If you are referring to sharp corners, then I would focus on sharply trimming the edges of the cake. And use Sharon Zambitos technique for fondant on a square. I have also found that using ganache instead of BC will give you much sharper corners. Good luck!