As far as I know there is no option. C# creates Unicode applications.
The only reason to use multi byte would be supporting Windows 9x. But even that can use Unicode with an additional DLL.
If you want to access files with multi byte encoding use the
Encoding Class (System.Text)[
^] to convert text (e.g. read MBCS file binary, convert to Unicode, process, convert back to MBCS, write binary).