(a) exposes some settings of the ChromiumPortable.exe launcher. Usually this is the one you're looking for.
(b) defines what the launcher does (which executable it launches, how to fix paths in the preferences file etc.). You'll only need to modify it in case of a customized install (e.g. you removed the 32- or 64-bit build to save space), but it'll be overwritten during upgrades.
(c) is used by the launcher to store its state. You shouldn't normally need to edit it.