I do not really understand what you did with that power symbol.
I think you mean a local power Symbol. And yes, I think I agree that having local power symbols is the only real solution.
For me, the answer is also partly academic. The schematic looks pretty clean and simple at the moment. The main sheet has a regular GND and +5V power supply, and on it are a few instances of a hierarchical sheet which just has 3 hierarchical pins:
.
And then, on the hierarchical sheet, an on/off switch powered by the global +5V & GND, then an B0505 1Watt SMPS module, some filtering with a capacitance multiplier and a cheap HX711 module. (Schematic is not finished yet, so don’t bother with details).
Below that 2 opto couplers to get the data out of the module.
Working with only local labels for the isolated power works for now, but I have plans for more elaborate isolated modules later, and it would be nice to have a better solution then.