Desoldering the 0 ohm resistor is the best way to decouple the 5V coming from OSPi with 5V coming from USB. However, in most cases it’s fine if you don’t desolder the 0 ohm resistor. The reason is that these different 5V power sources are all based on switching power circuit, which means there is a feedback loop that monitor’s the actual voltage on the 5V line — if the voltage is higher than the internal reference, that particular switching power circuit will turn off. So whichever 5V power source is outputting the highest voltage will take over. For example, if the USB adapter normally outputs 5.01V, and OSPi’s switching circuit normally outputs 4.97V, when they are put together, USB will take over as it has the highest voltage.