Hello Amit,
Here is the Android library project for unity Push.
You have to customize "onMessage" method of App42GCMService.java file and rebuild the library project and update app42pushservice.jar file with this in your Android plugin folder.
Similarly you have to make changes in other plugin Service as well. But As per my understanding is concern while sending message from AppHQ it also receives by other plugin as you mentioned because message is not in appropriate format required by other plugin, application crashed.
Please make these changes & let me know if it helps.
Vishnu