There are plenty of tuning kits and ECU maps, along with piggyback boxes on the market for the 1.3 multijet engine, and the only thing to really look out for is to stick to reputable brands and services.
That being said, the gearbox, clutch and pressure plate, and the 4x4 system as a whole is probably capped at capacity for around 200Nm of torque, which means anything more might break something quite expensive.