This example opens Flashupdate.exe when any *.os File is double-clicked:
[HKEY_CLASSES_ROOT\.os] @="OsUpdate" [HKEY_CLASSES_ROOT\OsUpdate] @="OS-Updatefile" [HKEY_CLASSES_ROOT\OsUpdate\defaultIcon] @="FlashUpdate.exe,0" [HKEY_CLASSES_ROOT\OsUpdate\shell] [HKEY_CLASSES_ROOT\OsUpdate\shell\open] [HKEY_CLASSES_ROOT\OsUpdate\shell\open\command] @="\\Windows\\FlashUpdate.exe /UO /F\"%1\" /Y /RC /Q /V3"