I don't think that the user can adjust the charge rate. On my Prius Prime, which has a 3.3 kW charger (probably the same one that's in the base model Rav4 Prime), there are two modes, and which one is used is determined automatically by the battery management computer, according to the voltage of the power source: 1. If the car is plugged into a 120 volt (L1) supply, the charger will attempt to draw 13 amps from the circuit. This is about the maximum that can be drawn continuously over an extended period of several hours, without heating a 15 amp circuit breaker or fuse to the point where it might pop in a slight surge or ripple appears in the circuit. Most 120 volt outlets in your home are fed through 15 amp circuits. 13 amps at 120 volts = 1,560 watts, about as much as an electric bathroom heater or microwave oven on full power, and it takes about 5-1/2 hours to charge the 8 kW-hr battery in my Prius Prime with the L1 charger that came with the car. The much larger Rav4 Prime battery probably tales at least 11 hours to charge on a 120 volt circuit. 2. If the charger detects 240 volts incoming, i.e. an L2 charger, it will still limit itself to 13 amps (3,300 watts) to prevent tripping a 15 amp circuit breaker if that's what the supply circuit is equipped with. Now, it is possible to buy an L2 charger that can deliver 27 amps (6,600 watts) - you can find them on Amazon for about $350 - but these won't do you any good on a Prius Prime or Rav4 Prime that has only a 3,300 watt charger. The 3,300 watt charger will not draw more than 13 amps even if supplied from a 30 amp or 40 amp L2 charging station. I've proved this on my Prius Prime: there are public 30 amp and 40 amp L2 charging stations at the SMUD Headquarters building, but my Prius Prime still takes 2 hours to charge, same as with my 13 amp L2 charger at home. A 30 amp L2 charger will only actually benefit you if you buy a Rav4 Prime XSE with the Premium package and the 6,600 watt charger, or a car like a Tesla or a Chrysler Pacifica, that has a 6,600 watt charger as standard equipment.

NOTE: If you need to use an extension cord with the L1 charger that came with your car, this can be done if you are careful to observe the following: Use a 10-gauge copper-conductor extension ONLY, !2 Gauge extension cords, or cheap aluminum conductor ones, will get hot and cause too much voltage loss. NEVER use an extension cord, even a 10 gauge one, that's longer than 25 feet. The prongs on the extension cord connectors must be clean and not corroded. If the connectors or the cord feel unusually warm after 10 minutes, stop - there is too much resistance and therefore too much voltage loss. I've used a 10 gauge, 25' extension cord a couple of times with no problem, when when I couldn't park close enough to an outlet to reach it without using a short extension cord. Toyota does not recommend using an extension cord at all, so I would only do it in emergencies and not make it a regular thing.

As for the relative risks of "quick charging" vs slow charging, I've almost always charged my Prius Prime on 240 volt L2 chargers, and it's showed no sign of battery degradation in the two years/16,000 miles I've owned it. The battery is actually doing BETTER now than it did when I first bought the car. In the first 12 months, it was only giving me 30 miles of range. In the second 12 months, it's giving me about 33 miles in winter (average temp 45°F), and 37 miles in summer (average temp 90°F). So the use of a 240 volt, 3,300 watt charger doesn't seem to be hurting it any.