Change Default Program for file - Command line or Registry

Please follow the steps.

1. Open an elevated command promote(Run as Administrator).
2. Use FTYPE {fileType}={commandString} to creat a file type and associated command to open the file.
3. Use ASSOC {.fileExtension}={fileType}

For example:

assoc .txt=txtfile

ftype txtfile=c:Program FilesWindows NTAccessorieswordpad.exe "%1"