When Microsoft Edge reaches general availability in January, the browser will automatically be installed on Windows 10 devices via Windows Update. Microsoft has added a new Registry value to Windows 10 that blocks the automatic install of the new Microsoft Edge browser. The new value needs to be created under the HKEY_LOCAL_MACHINESOFTWAREMicrosoftEdgeUpdate key and is called DoNotUpdateToEdgeWithChromium. The Blocker Toolkit includes HTML instructions, a CMD script, and Group Policy templates.
Source: https://www.bleepingcomputer.com/news/microsoft/how-to-block-windows-10-update-force-installing-the-new-edge-browser/