I'm not sure this is what he asked. or maybe I'm wrong, as he didn't really explain what he wants.
he/you want to make a forwarder, or a channel forwarder?
the forwarder is a dol, which you can launch from hbc to test. the channel is only the external cover for you to launch your forwarder (the homebrew) from system menu.
if you want to unpack/repack a wad, then customizeMii is the right tool
if you want to edit/create an animated banner, customizeMii is not allowing that, you need to learn how banners are working.
if you want your forwarder to forward to a specific path (sd and/or usb), then customizeMii is not the tool either, it only pack files together, it doesn't compile source code. for that, you need to learn how to code and compile sources with devkitpro to generate a dol file that you can pack into a wad.
I replied to a similar thread few days ago, was it for you too? I added links to all needed tools and guides.