If you somehow figured out the way you could add values, perhaps you could just link the change in esterus value to the event of when you get ejaculated in (which by default causes you to gain semen and sedation souls).
Which software are you using to edit those game files, would love to try doing some modding myself.
It's a bit complicated and takes some Japanese knowledge, but here it is:
To extract the contents of the .wolf file type, download touhouSE. Click and drag the .wolf file in question (BasicData.wolf) on to touhouSE.exe and hit Enter to extract the contents to the "data" folder that goes with touhouSE.
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Click ダウンロード in the top right corner to get it.
Next use Wolf RPG Editor. There is an English translation out there, but I wasn't able to get it to work, and Japanese isn't too much of a problem for me.
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When you extract the editor it will come with an example game preloaded. Delete the contents of the BasicData folder and replace them with the contents of the above "data" folder.
Open up the editor. The internal values of the game can be found in the third menu option at the top (表示(V)). The simple item changes occurred under ユーザーデータベース (user database) and then 2: アイテム (Item) under タイプ. You can only really change the purchase price here, which automatically affects the sell price.
The more complicated changes all occurred under the 表示(V) -> コモンイベント (common event). Waterspoon doesn't use the built in functions for HP or SP at all. He created his own classes and functions for all values in the game, so anything that affects them have to be changed in the corresponding sections of this event list. Many of the relevant changes occur between events 838 and 848. Event 839 handles getting Sedation Souls, and 840 handles using them. You can compare the original game data to what I did for reference. Keep in mind that if an NPC says a value in a speech box, you'll need to change that value there as well.
Most of the internals are in Japanese, because this is Waterspoon's work. And it is all very detailed and impressive. I doubt most RPG Maker titles have this many internal events.
Finally, once you've made any changes you want, you'll need to recreate the BasicData.wolf package. In the main editor, choose the first menu ファイル(F) -> ゲームデータの作成 (File -> Game Data Prep). In the middle section, choose the third radial option, which will allow you to click on [BasicData] from the list. Hitting OK will generate BasicData.wolf for you to use.
