How to update Hosted Feature Service spatialReference with update_definition

[KeithLarson1]

Hello,

I am trying to update the definition of an existing Hosted Feature Service. I created a FeatureLayerCollection object from the item in ArcGIS Online and I am able to update some parts of the definition such as serviceDescription. However, when I try to update the spatialReference property, it returns {'success': True} without actually changing it. My guess is that it doesn't like that I'm passing it an object with another object in it, but I don't know any way around that. Here's a screenshot as an example.  

Does anyone know if I can update this, or am I out of luck?

Thanks,

Keith