No GeorgieB82, I don't believe anything has been done to allow additional levels although I imagine it would be an easy thing to add?
Keep in mind that you can change the reference levels without having any effect on the model. That way you can keep changing them to suit whatever you need to reference to at given time.
If you use "Sea Level" instead of Project Zero as your datum (as many people do ... and it does have its advantages), you technically gain a Reference Level slot.
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