No. I never tried it at all. The PowerBoost was delivered first in December, and at that time I knew I was about to get the new meter, so I never continued with this project.
But by looking at the display on the PowerBoost I can tell you that it reports negative values if I am selling power to the grid (I have solar PV).
If you have the same charger as I (Wallbox Pulsar) it is compatible with OCCP, wich you can find a custom integration for in HACS. Then you should be able to set max power. Or you can do it via the offical integration in HA. No need for you to build a Modbus node.
The downside of the official integration is that it is using the cloud service, which is a bit slow when you update the max power.