For the Raspberry Pi HAT, is there any need to disable the I2C fan control or other default HAT functionality since the board is only using the power pins, not the full 40-pin header?

May I ask where did you click to erase? Could you please point out the screenshot of where you clicked to erase and the error message when downloading? From my end, clicking on the erase option still allows me to download normally. nulls clash
RKDevTool-1.png
RKDevTool-2.png

When the 'Erase ...