Basically your approach isn't going to work exactly, as you have to alter the row's geometry object.Going to need to set !shape!.Z here, so maybe do it as a side effect of calculating some other field. For example, an expression ofCalcZ(!METERS!, !shape!)
and a codeblock of
def CalcZ(meter_length, shapeval):
shapeval.Z = 100
return meter_length
This would recalculate METERS to itself and as a side effect change the Z value to 100. Though this all feels like a somewhat indirect approach, you are likely much better off in just writing a short python script with an UpdateCursor as it'd be a lot more coherent and not many more lines of code.cur = arcpy.UpdateCursor(InputPointZ)
for row in cur:
row.shape.Z = 100
rows.updateRow(row)
del row, cur