There is a system register that is used to control pass-through mode, LW-9903.

When you write a 0 to the register, it is in normal pass-through mode and the HMI can still communicate with the PLC during pass-through (if allowed by the PLC driver).

Write a 1 to the register and it pauses pass-through, effectively turning it off.

Write a 3 to the register and pass-through is turned on but communications between the HMI and PLC are halted.