For completeness (and it case it helps someone else), I posted the source code here:

https://github.com/majbthrd/V2Gredux

The values in parameters.h can be adjusted, such as the EVSEMaximumVoltageLimit used in the ChargeParameterDiscoveryRes message.

Right or wrong, I went down the path of buying the Lumissil CG5317 eval kit and signing an NDA to get technical information.

My original aspiration was a CG5317-based sniffer with USB interface (I contributed the original RNDIS/ECM virtual Ethernet implementation for the TinyUSB open-source effort ...