I think you can put files in the iso directly.
But that may not work.
You can. Make sure the Project M files are in the correct place, put the cheats file in whatever folder your USB loader loads cheats from and load the game with cheats. It may not work 100% though, since there is one file that isn't being loaded that way (I forgot what exactly, but it's some Gecko OS thing that goes in SD root)
I imported a US Brawl from ebay for about $40NZD including shipping.
USB Loader GX supposedly makes use of that file.I think that would be gameconfig.txt
I bought it exclusively to install homebrew to play my PAL Wii games.u didn't have to u know iso