I bought that kit (2 of them) and I have 9 gallons of it fermenting in my basement fridge as we speak. Two 6.5 gallon carboys bubbling away at 55° on day three of fermentation. After primary fermentation is nearly done, I'm planning on doing a diacetyl "rest" (I prefer to call it a diacetyl "purge") and then I'll transfer it to secondary carboys and then begin to lager it down to lower temps, dropping a degree every day until I get to about 35° or so.
No "modifications" need to be done to a fridge to use it as a fermentation chamber. You can buy a single-stage temperature controller that the fridge plugs into. A probe connected to the controller goes into the fridge, and the controller turns on the fridge when it gets too warm inside.