Ah, unfortunately, there isn't yet a way to do so. We've been throwing around a few ideas here in the past, but the fundamental issue is that I originally wrote Pierogi as an experiment to create hierarchies of inter-related keysets. I've been leveraging C++'s class inheritance for this task, which means that adding a new keyset to the hierarchy takes a recompile. In theory, all I really need to do is to allow users to add a keyset _outside_ of the hierarchy, but I just haven't gotten around to it yet.

(Also, let me point out that Pierogi isn't the only IR control solution available for the N900; you can run the standard LIRC server directly, and Irreco/QtIrreco still works as a GUI on top of LIRC...)