I have a few ways of answering this. One is that styles are implemented in Python, so yes; a better one is that they are carefully set up so that someone can just copy-and-paste parts of existing styles without even knowing that they're looking at Python; an even better one is that learning Python in order to accomplish a particular style feature you want is better than learning BibTeX's style language or some domain-specific language I could make up. More people already know Python than could write a .bst file. And, like I said, I went out of my way when writing the style system to make it easy to compose different styles with only a couple lines of very simple code I could explain to someone who thinks Pythons are large snakes. In the end, though, you have to learn some language to do anything truly new, and I believe Python is a good choice.Does that mean I need to learn Python to be able to customize styles?
Robert