Add iPhone shutter count and serial number to EXIF data
No, Currently there are no apps which would be assigning shutter count / serial number etc. Apps like that would have to keep on working on background and then edit Metadata of photos. On iOS, editing photo would need user's permission and would trigger an alert view saying "Do you want app to allow modify the photo" etc.
So, creating such app is technically impossible on iOS without Jailbreaking. 

Also note:
There are apps like "EXIF Viewer by Fluntro", which allows you to view shutter count of photos you took on Nikon Camera etc. It also allows you to edit exif tags like Camera model, software etc.

Disclaimer: I have developed the EXIF Viewer by Fluntro App :)