best way to modify this would be using the super basic z-wave parameter tool Mike Maxwell provides:
https://community.hubitat.com/t/super-basic-z-wave-parameter-tool/3477
That way you can tweak the advanced parameters to your liking.
Edit: Looking at the manual for the Zooz 4-in-1, I don't a parameter for adjusting humidity offset, I believe the parameter you are talking about is for adjusting what percentage change must occur before humidity a humidity report is sent.
Humidity Sensor
Reports relative humidity.
Parameter 3: Use it to set humidity
percentage change to be reported by the
sensor.
Values: 1 - 50 where 1 stands for 1% and
50 stands for 50%. Default set to 10%.
Size: 1 byte dec.
Edit2: Rather than worrying about the actual accuracy of the Zooz sensor perhaps you can just account for it in your rules the control the humidifiers?
I do this with my rules that control my bathroom fans, I have them turn on/off based on the measured humidity of the bathroom sensor and a "base-line" sensor that is located outside of the bathrooms not affected by the humidity of the showers.