Yes, you can.

But the money you would spend would never justify the additional power you would gain.

If you are that hungry for power don't reinvent the wheel. Sell the car. Buy a newer 535i and then take advantage of the software changes you can make to a stock 535i and you will still be money ahead.

I agree, 535i with tune only makes almost 400hp, with minor bolt ons 450+ is easy. You can barely get 330hp out of a supercharged n52. Just not worth the money.