Notation on schematic for circuit with n-channel switch
If I understand correctly, you are asking what to call the net on the drain of your low-side N FET and what to call the net on the source of that transistor, correct? That's very fine to do, but check my warning further down about the danger of accidentally bypassing the transistor.

I would call the GND that is connected to the source of your transistor as "the" power GND. I would assign a net-name to the node on the drain as "LOW_SIDE_LOAD" or similar. I would not give it its own GND symbol unless it is truly spanning multiple sheets. If it is, I would have one schematic sheet with a large square drawn around the circuit element that connects it to GND through your FET. As an engineer I generally follow GND on a schematic to its source, which is usually the power supply page that ends in a connector of some type. If I saw some other GND symbol, I would follow it through the schematic until I find the tie / relationship to GND.

You should try to make it as clear as possible that any other connection between LOW_SIDE_LOAD and GND will effectively bypass your switch. This is one of the dangers of low-side switching.