Is it safe to use modbus functions in secondary program?

Hello,

In several modbus functions - for example modbus_get_signal_status - there is a boolean parameter called “is_secondary_program”
The URScript Manual says:
is_secondary_program: A boolean for internal use only. Must be set to False

Is it safe to use modbus functions from the secondary program?
If yes: should the is_secondary_program parameter be set to True even if the documentation says “Must be set to False” ?

Thanks
Csaba