Hi Widenliu. It solely depends on the version of your Windows version. Windows OEM version allows you to change CPU, HDD(it has to be cloned to a new drive first to keep your activation as it copies the installed software OS hardware id of your current) but you will loose activation if you change your motherboard. Windows Retail Versions offers more flexibility as it allows you re-install an re-activate on line or call MS support for a new key as long it installed only in one machine.
Moving from 1950X to 2990WX, the OS will consider it still a single CPU. As for experience, I have a Ryzen 7 system that started with a 1700 to 1700x on the same Asrock AB350, Intel 600P NvMe and it did not need any re-activation.