Here are some quick notes of how to use other people’s work on Github when building unofficial Cyanogenmod or other custom Android builds.
Many unofficial device maintainers have a local_manifests xml file, which specifies replacement projects. See some documentation about local_manifests here: http://wiki.cyanogenmod.org/w/Doc:_Using_manifests
This modifies the repo command to tell it to pull in altered projects that should replace or add to the original set of projects you are working off, such as device specific files. Example here: https://github.com/bleached/android_local_manifest
Next, you want to look for the build patches, which maintainers typically put in the device specific folders (from the root folder, look in device common or the by the actual device name). For example, some maintainers may place the patches here: https://github.com/bleached/android_device_samsung_msm7x27a-common/tree/cm-10.1/patches
Ultimately how this is organized will vary by the maintainer.