arcpy: changing a grid spatial projection in a layout

[PeterKT]

I have a UTM grid within my map frame, and I would like to use arcpy to change its projection.

As far as I can see that can only be done with a CIM definition.

I'm getting an error. Any ideas? Or am I on the wrong path?

....

cim_mapframe = first_mapframe.getDefinition('V3')

cim_mapframe.grids[0].projectedCoordinateSystem = arcpy.SpatialReference(7854)

first_mapframe.setDefinition(cim_mapframe)

I get an error when on the setDefinition line. 

AttributeError: SpatialReference: Get attribute X does not exist

[DanielGarcia]

Hi Peter,

Please try using this...

cim.grids[0].projectedCoordinateSystem = {'wkid': 7854, 'latestWkid': 7854}

This work for me.