Well, the easiest way that I found is simply opening the file "chXY.rpy" in game folder with notepad++ and then studying the sections for each day or event.
For example if you see a line "MCDick=1" then that means that it will be called at some point by another event script as a condition . For example if an event has conditions "MCDick=1" and "else" you can use that to influence the game to your desire. The game Babysitter is an amazing teacher for that cause it's easy to read through. There was actually a condition that was exactly that "MCDick", so I'm using that as example.
Then you can use those conditions in the game with UnRen itself. It's basically cheats to force certain events to happen. Tbh, I have not really gone through this game's script to really know what's going on.
It's easy to use them, for example.
Let's say MCDick is tied to Kari seeing MC naked. A few days later she is gossiping with Lois about dicks (this is completely fictional, btw., I know Kari would probably cut her own tongue out than talk about her man's dick with LOIS of all people, she is way too possessive) and the event script has too options. Either Kari has seen it or not. If she did, she can daydream about his size, if she didn't she can be a clueless virgin. So, if you want her to daydream, just press Shift+O to open Unren BEFORE IT COMES TO THAT POINT in convo and simply type "MCDick=1" without quote marks. That enables the condition and now Kari has seen him naked, even though she hadn't.
It's basically the same for every condition. But since I haven't checked Roommates' script file I can't say for sure what conditions it uses.
If you want to learn how to use UnRen and you have time, I really suggest getting Babysitter (the first game) and Notepad++ (it's free) and just submerging yourself in the file and experiment. Note that in that game the only file that matters is scripts.rpy and some of the most important conditions are Horny=(number), Friend=(number), Money=(number) etc.
!!! Pay attention to capital letters, they are extremely important. If for example the script call for money cheat is Money=1000 and you write money=1000 it will not work.