According to the specified value, I have byte 97, while in your version it's 98 (+1). It's not entirely clear why it's 97+, and not 353 - 354.
I've attached the modified file that I used, changing the extension from zip to h5u. I added extra spells, but they didn't appear anywhere. Maybe you just need to replace the XML file in the data folder, and not add a new h5u file. Maybe I missed something, or maybe it's not working, or maybe the byte is incorrect?