In article ,
says...
I'd like to replace my cartridges with plain ol' cotton batting, but of course
my Penguin manual says their cartridges are essential.

Well, they would say that, wouldn't they, seeing as they make
a ridiculous amount of money off them. :-)


Would removing the carbon be harmful or not?

Heavens no, no harm at all.

Should I stagger their removal (have 3 total in 2 different filters)?

I wouldn't bother with that. If you've been replacing them as
per the manufacturer's directions, they're not involved in the
biological filtration, so they can just leave. Your biowheels
probably can carry the load just fine.
G