One simple way to do it is to search your module scripts for "satyr" or other similar subrace that is used by the system that is somewhat unique.
That will return all scripts that reference that subrace. Look through each script - even it if isn't specifically part of the subrace system script set...other changes might have been made to other scripts to enable specific abilities or other ways to handle the subrace.
In each script, see how the "satyr" race is handled. Copy that relevant line or code block and add paste a set block beneath the one for the 'satyr' and then begin to customize it with how you want your subrace to be handled (positive/negative effects, stat boosts, etc...)
Make sure you comment your new additions well to note that these are specific to your module and what subrace you're adding (so that if you need to search in the future for your edits or that subrace, you can do so easily).
Lastly, document every step - what scripts you had to modify and how they work together (this script calls this other script, etc...). Keep that reference sheet for when you want to add other subraces in the future.
Adding a subrace should be relatively simple in that fashion.
