Custom resource folder in Android's APK File

We are integrating a third party ads library to our games and it uses a custom resources folder called "ad_resources" that is at the "root" of the app. This resources folder has some uncompressed images as well as a javascript file that Unity cannot compile. I cannot add a custom path for the resurces since it's embedded into the third party jar. is there a way to add these resources right after building but before the apk file is complete?