##No
No
You can't save data on the xbox via the content pipeline.
You can however use other methods (standard .net once you've got a file stream). See here for an example: https://stackoverflow.com/questions/3723287/good-example-of-xna-4-0-to-save-game-data
See also: http://robotfootgames.com/xna-tutorials/92-xna-tutorial-savingloading-on-xbox-360-40
The content pipeline is for build time files (they are compiled).
See What is the content pipeline (MSDN).
It works well when you want to perform a lot of pre-processing to go from your original file (maybe an image file) to your runtime class (like a Texture2D with mipmap levels), but that's not the only way to load files on the xbox (so you don't have to save to the XNB format).