Yes, in fact fwtool used to be at the base of 3DS kernel downgrading via hacked DSiware transfer (back when that was a thing)
TwlMenu++ or whatever it's called is probably the most updated DSi-mode homebrew (and more) launcher
You can also simply convert nds/srl/app to cia and install them directly on Home, but not all DSi-mode homebrews are designed to be run that way