I hope you are also running a VPN on your Windows box because if you think just changing the TTL is enough for the vendor to know that you are not tethering......
There are many other ways for them to know your traffic is coming from a computer and not a phone. If you've ever monitored a Windows computer connected to the internet you'll notice that it constantly hits sites like windowsupdate.com, time.microsoft.com, ctldl.windowsupdate.com, etc. Not easy to turn these off. A smartphone would never reach out to these websites.
The question is do mobile networks even bother looking for these types of anomalies?
All the years, my carriers never detected. (Ok, all my devices are Android, Macbook, or Linux & FreeBSD) -- but if one would be paranoid, you could edit your hosts file (in Windows it's C:\Windows\System32\Drivers\etc\hosts) and make an an entry
127.0.0.1 windowsupdate.com
127.0.0.1 time.microsoft.com
and problem solved. Windows updates can be definitely paused in the system settings, and I am sure there are settings to prevent updates over Wifi.