I'd go easy. The 1.9 TDi is available in much higher outputs in lighter veicles and there's a reason the heavy vehicles are fitted with the lower powered versions,

A bump in torque and horsepower will be fine for a bit of acceleration, but don't use it as an excuse to select a gear for the day. Increasing power and torque is easy. Gains in fuel economy are much harder to achieve. They'll get a bit by advancing the injection timing and reducing EGR but don't expect much in the way of economy. If you're running the engine hard, more frequent oil changes would be advisable.