How would I go about modding a Brawl ISO?

[Xero874]

So, basically, I'm trying to add custom textures to this modded Brawl ISO with Project M on it, but basically when I try to replace a CSP in brawl box, and replace it in WiiScrubber, it says it can't find free space.
The file is exactly the same size as it was before.
So is there any tutorials on how to go about doing this?

[Xero874]

Thanks for the help, guys! -.-

[Xero874]

bump.