In the Business Analyst Territory Solution, there is an Edit Territories subsection. There doesn't seem to much information about it, but I would need to find its syntax. Does it even exist?
Wandering around in the Help documentation took a while even for me before I found basically the section that references these functions. It is the last section at this help link basically.
Create Manual Territories
Territory Solution—ArcGIS Pro | Documentation
The complete Territory Design toolset functionality-wise is still on the ArcGIS Business Analyst Desktop side so if someone is serious about this still set could recommend starting there first as there are several TS solution types.
Here are some syntax references for Territory Design toolbox:
An overview of the Analysis toolset—Territory Design Toolbox | Documentation
I have looked at that documentation as well, but there does not seem to be any information about it.