(defun dpbs (initial-value
             &rest where-and-what)
  (loop
    :for (where what) :on where-and-what :by (function cddr)
    :do (setf initial-value (dpb what where initial-value))
    :finally (return initial-value)))


(let ((n #xA1B2C3D4))
  (format t "~x~%" (dpbs (ldb (byte 8 24) n)
                         (byte 8  8) (ldb (byte 8 16) n)
                         (byte 8 16) (ldb (byte 8  8) n)
                         (byte 8 24) (ldb (byte 8  0) n))))
--> D4C3B2A1
    nil