* (uiop:with-output-file (s #P"/tmp/blah.txt" :element-type '(unsigned-byte 8) :if-exists :supersede)
    (write-byte 1 s)
    (setf (stream-element-type s) 'character)
    (write-char #\a s))
#\a

* (uiop:with-input-file (s #P"/tmp/blah.txt" :element-type '(unsigned-byte 8))
    (format t "~A ~A~%" (read-byte s) (progn (setf (stream-element-type s) 'character) (read-char s))))
1 a