Hello, I'm new there; excuseme if my english isn't good.

I'm trying to mod SSBB (NTSC) by replacing Pit with Waluigi.
I have to edit the iso itself as I play SSBB with Dolphin.
I used WiiBaFu to extract the iso, replaced all the files except the CSS images and life icons and then recreated the iso.
I tried the game and it worked.
Then I used BrawlBox to edit sc_selcharacter_en.pac and replaced the textures and converted the extracted files back to iso again. This time the game crashed when I went to the selection screen (I choose training mode). I tried many times, I tried using a file smaller (in size) than the one I exported from the .pac file too.
I know this was yet asked but I couldn't find any good answer.
P.S.:I'm a N00B! This is the first hack I tried to install.
EDIT: The hack I'm trying to install is the one that overwrites Pit:
http://forums.kc-mm.com/index.php?topic=34126.0