Yes, you can get a different spec for the sidewall, provided
that your wheelwell can accomodate the changes.
If you upsize too much, the tires will rub against the wheelwell,
esp. if the car is really loaded, going over humps. Font tyres may
even rub when the steering is turned lock-to-lock.
As performance, I think it will affect both performance and FC
adversely, because the tire is now bigger. Your speedo and odometer
accuracy will also be affected
