Windows 10 contains programs, such as Notepad and Task Manager, that we have come to love and use often as part of our daily use of a Windows computer. Sometimes, though, you may find that you want to replace these programs with more feature-rich third-party programs, but still be able to launch them like you have gotten used to. To do this, we can use the Image File Execution Options Registry Registry Registry key to make Windows launch a third party program whenever Microsoft Notepad or the Windows Calculator is launched.
Source: https://www.bleepingcomputer.com/news/microsoft/how-to-replace-windows-10-system-programs-with-non-microsoft-apps/