I like it when a program's content can be extended easily.
What do you think of a fundamentally different approach that doesn't use a central file at all? Each style could have its own main file that contains name, path info etc. Each style class is then just a list of the styles' filenames. The program itself performs a search for style classes and standalone styles in one of its subdirectories. This might be done whenever it is run; searching a single directory of such size is fast.
This would eliminate the wuss of maintaining a central file (I took a long time getting it to work). The cost is that styles need an extra file each, or at least each style class needs a file if you modify the idea a bit. But according to Dullstar, it is current practice already to ship a LemmixStyles.ini with one's styles.
Your idea appears to be a compromise between extendability on the one hand and simpleness of the data on the other hand. I'd like to wait for other people who worked more with Lemmix to comment on that. I've set up Lemmix only once, and only with the Genesis L1 styles.
-- Simon