If you do have questions regarding this, my Discord is the place to ask. Modifying and expanding BMS for your own personal use is still greatly encouraged (it will expand your BGS modding knowledge and promote growth on this subject), just know I do not have any up-to-date documentation to aid you. Between my more limited time and growing pressures to finish BMS, I am not in a position to take this up now however.
One day, I would like to filter through this information and create pages with descriptions for mods included in BMS and how to better utilize and edit the modlist for those of you keen on modifying and expanding it based on your one personal tastes. While yes, it can still be used by those of you more interested in reading the nitty gritty, note that it is incomplete and I am not actively focusing my limited time on supporting it. All information beyond this point is on the outdated side.