This is one way:
(defun c:rx ()
(setq RLXR (getstring "\nName of External Reference to reload: "))
(command "_xref" "r" RLXR)(princ)
)
Another would be to open the XREF dialog box, click on the XREF which has the path you want to change, then delete the path information in the "Xref found at:" box, and press "Save Path".
There may be other ways, always open for better and more elegant.
Sorry, you have to open each drawing separately tho.