DualUse with modifiers applied?

I’m interested in the DualUse plugin, but it seems fairly limited in what it can do. In particular, I want my left Fn key to switch layers when held, and to issue LGUI(Key_LeftBracket) when struck (browser back in Safari). Per reading the DualUse docs, however, it seems that’s not possible—the key invoked must be a single, unmodified key.

Is this correct, or is there a way to get this working?

It is correct, DualUse can’t support modified keys, because those use more bits than what we have available. You may want to have a look at the SpaceCadet plugin, which does something very similar, in a different way, and supports modified keys.