Split APK Tools

Prereqs

python with BeautifulSoup4 (+ parser) and wrapt (pip install BeautifulSoup4 lxml wrapt)
up-to-date apktool on PATH
adb on PATH with target device connected (root not required)
Android SDK Build Tools (Android\Sdk\build-tools<version>) on PATH

install desired app on target device (eg from play store)
python PREPARE.py com.my.package: pulls split apk, combines into base folder, applies network security config patch and some fixes, saves package name in package_name.txt
edit code or resources in base directory
python SEND.py: repackages, signs, and installs apk (uninstalls current version, then installs modded apk)
python CLEAN.py: removes temporary files to prepare for modding new app