Modifying the Shiny Rate in HG

[FireStorm]

Hello, 

Recently I have been attempting to raise the shiny rate for HeartGold to about 1/100, however after some research throughout this forum and finding what seemed to be a good guide on how to raise the chance to ~1/257, I thought that was fine. However, every time I go into my hex editor and modify offset 0x70080 in arm9.bin (specifically, I modified it from 08 to FF), the hex that should contain the shiny rate for my game, upon patching the ROM together and loading it in an emulator, it crashes in the title screen, with the bottom screen a solid black and the upper screen the missing the title, but has the background. Is there something I am doing wrong?

Link to guide I used: https://projectpokemon.org/home/forums/topic/33193-tutorialhgss-change-the-shiny-probability/

Thanks in advance!