You wouldn't need to touch BSPs or drivers unless you're doing bringup or updating the Android kernel for a supported device. The common approach to avoid a lot of pain whn updating Android is to simply stay on the old kernel supported by the OEM or partner.

Unless you are actually shipping a custom device running Android, there's very little reason for most developers to poke that far down the stack

This acronym is somewhat known in Android device hacking communities that try to replace Android with Linux or Windows, because these communities usually deal with understanding the bootloader and Qualcomm distributes bootloader sources from what I remember in their BSP.