FWIW, it sounds like you aren't really saying why you want to do this. The regen and battery heating sound like questionable differences. Small differences if even that. Youtr SR+ floor mats and sound system can be upgraded without spending much. In reality, the Premium Sound System is not all that Premium. Todays' electronics are good. The SR+ is really mostly missing the (small) powered subwoofer, and that can be remedied for ~ $150 and some simple wiring work. There are those tiny tweeters up front that you could also add cheaply. Even if you paid a car audio con artist to do it, it's not very much.
So all in all it sounds like a huge money hit for exactly what? Why are you even considering this, honestly? If you really need the bigger battery, did you only now realize it? If it's for the rush, and you can afford it, OK, sure, but you may as well swallow the loss, stop pussyfooting around and get a real Performance 3 or Y with all the automation, or you'll want more and the car will be worth less in resale.
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