Yes, As long as it's an NTSC iso of Brawl. Just copy RSBE01.gct from the codes folder in the SD root, to the codes folder in your usb-loader folder.
That method only seems to work on USB Loader GX for me. Wiiflow and CFG USB Loader doesn't seem to apply the codes properly and the game will freeze on either the character selection screen or the stage selection screen. I would recommend USB Loader GX for Project M anytime you want to play it.