The mulch kit comes with blades and front baffles. You simply bolt the baffles into place - ExMark's instructions are simple enough that even I was able to do it w/o help, and that's saying something. Once everything is installed you won't be able to side-discharge. You'd have to remove the baffles to do it.
OCD is operator controlled discharge, a solution that should have been introduced a long time ago. It let's you manually change from mulching to side-discharge on the fly. More expensive but absolutely worth it.