I think what you're looking for is ScriptableObject. When you implement ScriptableObject you can create instances of those objects via editor scripts and use those objects e.g. for storing data.

I'm using this, for example, to store meta information about my levels persistently as objects in the project. Here's a script snippet I used to create those assets ("LevelData" is a ScriptableObject).

[MenuItem("LevelEditor/Create Level Data")]
public static void CreateLevelData() {
    LevelData asset = new LevelData();  //scriptable object
    AssetUtility.CreateAsset(asset, "LevelData New");
    AssetUtility.SaveAsset(asset);
    EditorUtility.FocusProjectWindow();
    Selection.activeObject = asset;
}