This is in the pipeline. Kind of. I'l explain.
Problems like this are easy to solve for specific cases, but hard to solve in the general case. Which means it's easy to add a specific test for astaroth and the fertility potion, but harder to set up a system that allows you to add arbitrary effects as new girls/items/traits enter the picture.
Additionally, adding in lots of special case code is a maintenance nightmare, so we don't want to do that if we can avoid it.
The good news is that the Lua scripting I'm busy knocking the bugs out of should allow things like events that fire on gaining or losing a trait, or equipping an item. So you'll be able to write an event for Astaroth that fires when her traits change, see if she's gained or lost sterility, and tweak her stats accordingly.
And that will give us our general case solution, since you'll be able to add the handling for these cases to the girlsx file.