Core Data : When is the point of no return with adding attributes ?

If by versioning you mean creating a new version of the Core Data model, create a new version of the data model when you reach the point in development that you want to keep the existing data in your app. In the early stages of making your app it's easier to trash the existing Core Data store (file) and starting with a fresh store. Eventually you will hit a point where starting with a fresh store causes problems, such as when other people start using your app. That's when you need to create a new version of the model and migrate from the old version to the new version.

@ szymczyk,
I must tell you first, i'm not a professional, mathematic is the apple of my eye since I'm no more working for bread and butter.
So it is, I assume trashing would be the easier solution if I would know how.
Maybe you or you has an explanation (a link ?) in detail how to do this.

For an iOS app deleting the app and reinstalling it will trash the existing data.

For a Mac app, the Core Data store is in the Application Support folder. For a Core Data app of mine, the file has the extension .storedata. Move the store file to the Trash to delete it.

Yesterday I found in Application Support/CallHistoryDB:

Multiline
CallHistory.storedata
CallHistory.storedata-shm
CallHistory.storedata-wal
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I moved the folder to an external device and killed the original.

I setup a new project StoreData, killed the StoreData.xcdatamodeld and replaced it with the model of my project.
This works, but before a must Sandbox uncheck.

Sorry, wrong button pressed.