What happens in background when an app is linked or unlinked to/from Play Store? If you are rooted, you can use Titanium Backup to link or unlink an app to/from Play Store. What does Titanium Backup do for it? I don't think Android API supports this directly. It alters a file or database or something else?
I am just curious...
It removes the app's entry from the /data/data/com.android.vending/databases/localappstate.db database:

root@android:/data/data/com.android.vending/databases # ls
library.db
library.db-journal
localappstate.db
market_assets.db-journal
suggestions.db
suggestions.db-journal
appstate.db
root@android:/data/data/com.android.vending/databases # sqlite3 localappstate.db
SQLite version 3.7.4
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite&gt; select * from appstate where package_name='com.android.chrome';
com.android.chrome|2||||0|||&lt;myemail&gt;@gmail.com||

... Here I detached from the Market with Ti ...

sqlite&gt; select * from appstate where package_name='com.android.chrome';
sqlite&gt;


I'm not aware of it making any other modifications to the filesystem (it doesn't touch library.db insofar as I can tell), but it's possible that there's some other magic behind it.