u should be able to if u really want to use gateway. I was on gateway up to either the latest firmware or the second latest one. gateway doesn't work on version 3 and 4 of a9lh though afaik. u have to inject it into version 2 as well. with version 1, it works without issue. u may be able to inject it into versions 3 or 4 (sd-card less), but I don't know for sure about that. like the others who've posted in this thread, it's really not worth it.
edit: oh, and btw, firmware and 3ds type shouldn't matter. it's the a9lh version that does.