I am certainly no great cheese maker, but I would be surprised if you had trouble getting shop bought milk to separate into simple curds and whey.
The basic chemistry is that proteins have charges that repel each other, like magnets if you put the wrongs ends together. pH (lemon juice is the acid) alters the charge, and at a certain pH they have no nett charge at all, so they are no longer repelled. That is when they stick together and form curds. Not all proteins happen to coagulate at acid pH, so they stay soluble in the whey - hence the term "whey protein". I love a bit of chemistry in the kitchen
Re: homogenisation, the formation of curds is driven by protein coagulation, so the cream should not interfere much one way or the other. Probably even skim milk would work.
Re: pasteurisation, it may well alter protein structure a little, but not enough to stop it coagulating under acid conditions. Either way, this recipie starts with boiling. Pasteurisation is only heating to 80 C for 2 seconds (or 60 C for 30 min.)
Not making an apologetic for homegenisation and pasteurisation here, but it probably won't effect this one. If you can't get raw milk and want to add a little bit of life and enzymes back into it, get hold of some kefir grains and let them digest it for a little while after boiling (or, let them sit long enough to make their own acids, which will coagulate the milk without lemon juice).