I have been involved with tires and wheels to an extent at work for many years. The Prius specific issues are:
- changing any tire to a tire with an improved contact patch (better traction) is fine, however you will increase rolling resistance. This also may be worth it.
- changing the rolling radius, either by tire change alone or wheel and tire change is bad. This adversely affects ABS, TRAC, VSC, and the NAV system.
- changing to 16" or 17" wheels and tires is fine as long as you consider my previous two comments. As long as the increased diameter is offset by a lower tire profile and you will accept the increased rolling resistance, all is well if the rolling radius is within 2% of the original tires and wheels.
- The 44psi tire pressure may also be fine as reported by others. The key is to monitor your tire wear characteristics. If the tire is overinflated, by this I mean the pressure is less than or equal to the max sidewall rating when cold (undriven overnight) but greater than the OEM tire placard, the center tread area will wear faster than the outer tread area. If the tire is underinflated, the outer tread area will wear faster than the center tread area. Adjust the pressures until you get uniform wear across the tread.
The OEM pressure recommendation is a compromise of tire life, ride and handling, with emphasis on ride and handling. Many find the higher pressures offer a better ride with less sidewall deflection while improving fuel economy. Dealers are instructed, for liability reasons, to strongly encourage adherence to the tire placard. However, as I said, you may find higher pressures are more to your liking. DO NOT use lower pressures as you risk high tire temperatures and failure.
Personally, I find the 44 front/40 rear psi levels to improve ride and handling, and I do not see abnormal tire wear. However, my mileage is low and I will keep monitoring. I have done this on other vehicles for over 17 years with great success. It has also improved tire life.