Powering 4.6 V with 5 V USB power supply
Since the device will internally have a regulator to charge the internal battery, it's pretty certain that it can deal with a few percent of overvoltage.

You can certainly try a linear low-dropout regulator (LDO) to regulate the output to 4.7 V, but be aware that at the 900 mA specified, these 0.3 V drop amount to 270 mW of power, which can heat up the regulator significantly.

You could build a higher-efficiency switching regulator, but at output voltages this close to the input voltage, that's a complicated endeavour and I wouldn't recommend it. 

The switching regulators that you link to have a maximum duty cycle of 90%, which doesn't allow for conversion of 5 V down to 4.7 V.