The XL 824 is a strange beast. It’s certified as a Z wave controller, as you’ve noticed. It’s also a thermostat and it does support the Z wave thermostat commands, but there doesn’t appear to be any way for an outside controller to access them. The XL824 believes it’s going to be the primary controller and at the present time I think it will only talk to a Nexia bridge ( they are sister companies), and then only via the Nexia web portal.
I Believe @johnconstantelo was looking into it at one point, he has written the device type handler that works with some other trane models, so he may be able to say more.
Here’s the conformance statement for the device, you can see that it self identifies as a controller, not a thermostat.