I simply use http-request nodes to do whatever I need. I've not actually set/changed a schedule yet but I believe it to be possible the same as changing anything else like a setpoint on a specific device.
The Python API is a good source of info on working with the API and it certainly says you can change the schedule:
Haha, I note that the Python API actually references my blog post, that's funny. 
The Home Assistant Wiser repo has some more info on controlling schedules via the Python API.
This article has a good extended review that is worth reading as are the comments. In fact, the author asked me to collaborate on some additional articles but I really didn't have time to do them justice.
https://community.home-assistant.io/t/drayton-wiser/40358/28 also indicates that you can control schedules.
If I get any time, I'll have a go at some of this.
Oh, and the cloud part of the Wiser system is compatible with Alexa and Google Home. We can change the heat via GH.
Update: Just checked the Python API PR that added schedule handling and it all looks as straight-forward as I imagined it to be.
