Reduce 5v Trinket Pro to 3.3v?
The NRF24L01+ has inputs that are 5V tolerant! So you only need to provide 3.3V on the Vcc pin of the module, which you can do by putting a voltage regulator between it, and the 5V of the Trinket. So there isn't really any need to convert the Trinket to 3.3V.

PS Remember to add some capacitors to the output of the voltage regulator, as the NRF needs a pretty stable 3.3V. Noise in the power lines can cause instability in the operation of the device.