A (possibly useful) observation: the SDG1062X will set itself in HZ mode if the numeric entry is >= 1 000 000.
So, for example, if the free-form entry field is used to specify, say, 10 000 000 ohms (after changing the limits test boundary), the unit will display "Load: HZ". But the received message will still generate an error, of course, due to the non-numeric content.
Just passing this along as food for thought in case it simplifies at least the transmit side of things.