Valid circuit to drop voltage?
It's a perfectly &quot;valid&quot; way to do it, but it's probably a bad idea.
First, 4.2 volts across a 36 ohm resistor will draw about .12 amps, and the resistor will dissipate almost exactly 1/2 watt. If your resistor is getting very hot, it means that it's not rated for this power. A 1-watt resistor would appropriate.
Second, if the load can draw up to 2 amps, an increase of .12 amps will probably not overstress the power supply. That's only an increase of about 5%.
Third, you really need to check how the diode responds when the load (not just the 36 ohm resistor) is connected. Are  you sure the diode is rated for a constant 2+ amps? It may well get very hot and/or fail.
Finally, the load voltage will change somewhat as the load current varies (if it does). However, the voltage across D1 won't change a whole lot. Much will depend on whether the intended load has wildly varying current (less than 2 amps, of course), and depends on the power supply to stay constant.