I currently use USB Loader GX to load my ripped (and WIT modified) .iso
As long as your USB device has the necessary free space (and isn't listed as incompatible here:
https://wiki.gbatemp.net/wiki/USB_Devices_Compatibility_List), it should work.
USB Loader GX has the ability to read .iso from the SD slot but I haven't tested it (SDHC compatibility and read/write speed may be issues though). Using the SD card for Brawlex codes and files with a USB loader is not a problem though.
And I'd suggest looking to google for USB launcher installation instructions as they've likely changed since I installed mine.
