How to insert or build a customized module/binary to CoreOS partition (e.g. USR-A)?

[BING]

I'd like to insert a module (3rd party module, including bin,conf,and sourc files, not in upstream kernel module yet) to CoreOS system partition (e.g. USR-A), I just found there is "Custom ebuilds for CoreOS" https://github.com/coreos/coreos-overlay, so should I make changes to this folder in local machine before launching build? 

Also, Can I follow the instructions here https://coreos.com/docs/sdk-distributors/sdk/tips-and-tricks/ to do that (but my module is not "new upstream package") ? 

Sorry about that I didn't have experience at EBUILD previously. should I follow this guide  http://devmanual.gentoo.org/ for eBUILD? 

Thanks in advance