I don't know a lot about rpy
can you please put an example?
Okay, so I'm not playing the latest version here, but as an example take the "random_lists.rpy" file and open it with a text editor. Even basic old Notepad will do. Poke around a bit and look at the variables.
In this example, we're going to CTRL-F to find "list_of_tits" to see how breast sizes are assigned. As it happens, it's a weighted list, which means that the numeric value in a line like "list_of_tits.append(["AA",5])" means the likelihood of that size showing up as a percentile chance. The sum of the numbers in the whole group of lines don't have to add up to 100, but whatever the total is, size AA breasts will be 5 parts of that total. Think of the sum of the numbers being the denominator, and 5 is the numerator in a fraction. We could change that "5" to "100", and you've just increased the likelihood of the smallest size of breast by a factor of 20. You could zero out or assign a value of "1" to breast sizes you don't like to see to minimize their chance of showing up.
Another example in that same "random_lists.rpy" file is the body weight. I forget what the standard weighted chance for the "curvy" body is, but I changed that line in my game to "list_of_body_types.append(["curvy_body",1])" because I think that body type looks ugly. Don't like being called "Fuck Meat" as a nickname by the girls? Change the line "list_of_player_titles.append("Fuck Meat")" to "list_of_player_titles.append("Hot Stuff")".
Don't like that your sister is such a bitch at the beginning of the game? Change the numbers in the line that controls her starting stats. CTRL-F for "### LILY ###" and go down a few lines to the line of code that starts with "stat_array =". Her skills and starting behavior including love, sluttiness, obedience and happiness are right there.
The "script.rpy" file is full of things you can edit as well, but it's a much larger file and you have to wade through a ton of code. In this file you can change your starting money and a bunch of other factors and variables.
Between these two files you can change how likely certain hair colors and faces are to show up in random girls, change default starting happiness for new hires, change the age ranges, really just about anything.