APK Modification Specialist

I need an experienced developer to modify an existing APK file. The modifications include:

- Adding or removing features, specifically third-party integrations.
- Implementing in-app purchases as a new functionality module.

Ideal skills and experience:
- Proficiency in Android development and APK modification.
- Experience with integrating third-party services.
- Knowledge of implementing in-app purchase systems.

Please provide examples of similar work done.