Energy price per kWh modbus registers

In version 2.07 some new registers got added for energy price

  • Added Modbus TCP server registers: 5141 - Session saved cost and 5142–5143 - Energy price per kWh

By just using 5143 and doing price*1000 I can get it to set the current price, but how does that work in relation to register 5142?

And is it possible to also set negative prices?