No, you're right there OC. CFS, the Completely Fair Scheduler, is part of the kernel. You can change it to the Deadline Scheduler and maybe one or two others if you recompile the kernel. That's the mechanism that does the process switching in the background.
Nice and Priority are attributes that are part of what the scheduler uses to decide which thread context to load and run during any given time period.
I don't expect recompiling the kernel in a Unix environment is something that's actively encouraged on a regular basis, thanks to potential lost production and the proprietary nature of most mainframe operating systems so PG might not have done that as much. I don't know.

A suggestion regarding CEP2, it might be renicing itself apart from what it's parent process, BOINC, is doing. CEP2 might also benefit from higher priority in IO as well (man ionice to read about that one) given the huge amount of data it writes to it's own temp storage.