Is there any update on this thread?

Vuforia SDK v6.2.6 - Release Note says this

Vuforia is initialized and deinitialized only once per application instead of every scene

So my understanding is, if i save a User Defined Target, this will stay until i kill the app and even if i change to different scenes 

Oh, you mean regenerate it completely taking new image from the camera... Thanks.

Then I will use only one scene(what a mess!) until that feature is released.

You'll need to regenerate the UDT in the 2nd scene. They can't be persisted across scenes. This is a feature that we hope to enable in a future version of the SDK.

So, how to regenerate the target? I tried to save the trackableSource object generated from the camera image in the 1st scene to use it to create a new dataset in the 2nd scene and instantiate a new UDT, but when I set the dataset to active, the editor crashes :(

Here is my code, maybe you think it's an aberration:

public class CreaNuevoTrackeable : MonoBehaviour {
	
	private ImageTracker mImageTracker;
	private DataSet mDataSet;
	private TrackableSource mTrackableSource;
	private ImageTargetBehaviour ImageTargetTemplate;

	// SetTargetUser is an static class to keep the created objects.

	void Start () {
		mImageTracker = SetTargetUser.mImageTracker; //(ImageTracker)TrackerManager.Instance.GetTracker(Tracker.Type.IMAGE_TRACKER);
		
		mTrackableSource = SetTargetUser.mTrackableSource;
		
		ImageTargetBehaviour imageTargetCopy = (ImageTargetBehaviour)Instantiate(ImageTargetTemplate);
		
		mDataSet = mImageTracker.CreateDataSet();

		mDataSet.CreateTrackable(mTrackableSource, imageTargetCopy.gameObject);
		
		mImageTracker.ActivateDataSet(mDataSet);
		
		Destroy(gameobject);

	}
	
}

Thanks for your reply.

Maybe I explained wrong, actually I don't need to export anything(so the cloud thing would be a very extreme solution). I just need to create a trackable from the camera in the first scene to use it in the second scene. Maybe is there a way to re-use it to build a new UDT from the previusly created trackable?

I'll keep looking in the documentation and trying the code to understand how that works.

There is no way to export the trackable created by the UDT prefab, though you can submit the image to our Cloud Recognition service so that it can be re-used and shared. But in your case, I think that the easiest approach will be to use UDT in both scenes and to regenerate the target is the second scene.