One should be careful with this modification because of the Windows definition of process groups.

For example, if multi-threaded code thinks that by reading the value of the new os.cpu_count() it can use all the cores returned, by default it cannot as in windows processes by default can run only in a single process group (how it worked before).

We can see such code builtin python stdlib itself:
https://github.com/python/cpython/blob/bc61315377056fe362b744d9c44e17cd3178ce54/Lib/concurrent/futures/thread.py#L102

I think even .NET still uses the old way that python did until now:
https://github.com/dotnet/corefx/blob/aaaffdf7b8330846f6832f43700fbcc060460c9f/src/System.Runtime.Extensions/src/System/Environment.Windows.cs#L71

Although some of this stuff is used in code for python multiprocess code which that might actually get a boost (since different process can get scheduled to different groups)

https://msdn.microsoft.com/en-us/library/windows/desktop/dd405503(v=vs.85).aspx