Changing the TCP initial congestion window value in Windows 10

Question

I would like to do some testing with the TCP Initial congestion window on Windows 10 Pro, but it seems the settings are disabled in the Pro version:

Set-NetTCPSetting -SettingName InternetCustom -InitialCongestionWindow 64

Is there a workaround? Any tool that allows me to change the value?

I am getting the following error message in Windows PowerShell:

Set-NetTCPSetting : Property InitialCongestionWindow is read-only

I have a 500Mbit cable internet connection, and I often feel that the TCP Slow Start mechanism is throttling my bandwidth too much at the beginning of a download or speed test. It often takes up to 5-6 seconds until a download reaches the full 500Mbit/s speed. This might not be on my end, hence I would like to test with different InitialCongestionWindow-values.