Function: mm-set-buffer-file-coding-system

Set the file coding-system of the current buffer to CODING-SYSTEM.
This means that when you save the buffer, it will be converted
according to CODING-SYSTEM. For a list of possible values of
CODING-SYSTEM, use M-x list-coding-systems.

If CODING-SYSTEM leaves the text conversion unspecified, or if it leaves
the end-of-line conversion unspecified, FORCE controls what to do.
If FORCE is nil, get the unspecified aspect (or aspects) from the buffer's
previous `buffer-file-coding-system' value (if it is specified there).
Otherwise, leave it unspecified.

This marks the buffer modified so that the succeeding C-x C-s
surely saves the buffer with CODING-SYSTEM. From a program, if you
don't want to mark the buffer modified, specify t for NOMODIFY.
If you know exactly what coding system you want to use,
just set the variable `buffer-file-coding-system' directly.