Footbeds in boots for pros is pretty common. The guys at Sidas UK did them all for the Man city players a couple of seasons ago. A full custom will always be the best option but also the most expensive.
The superfeet carbon are a good call as they are pretty minimal. They are not an arch support though, instead they stabilize the rear foot which in turn helps stabilize the rest of the foot. Like any pre-made insole they wont work for everyone but in general they will be a lot better then the stock flat insole. Don't go modifying the Carbon cup on the base though as that is what gives the support, without that your essentially just using the same as what you already have.