Yes, but in this case it was a bit different
I was not creating a new stack: I was adding an already configured switch to an existing stack.
I made sure the firmware was all the same, powered down the stack (and the third switch), and then added the new switch by re-arranging the stacking cables in the correct order.
When the stack reloaded, I went to stack management and added the third switch to the existing stack.
Problem is, because the MAC address was lower on that switch, it took over the master role