Also- when does a component upgrade become a new PC?
I think it will depend on the licence. Last time I bought a licence was for Win8, so I’m not sure what the situation is now.
The most expensive licence is a consumer licence for people like gamers who constantly upgrade their machines. That can be shifted to a new machine without any problems.
Next is a consumer licence that is locked to a single machine. You can upgrade the machine, but there are limits to how many components you can upgrade within a time period. So, you might be able to put in a new motherboard, or a new graphics card, or a new HDD, but not all at the same time. However, apparently MS are pretty lenient about this and you can do the phone licensing thing to have it reactivated if you have problems.
Then there are OEM licences that large manufacturers buy. I think these are locked to specific hardware configurations, so you won’t be able to take a hard disk from a laptop and activate it on a completely different machine because the hardware configuration won’t match.