need a way to override defface?

[Drew Adams]

`setq' will override a value already given to a variable by `defvar' or
`defcustom', but is there a way to override a face already defined by
`defface'?  Interactively, you can use `C-M-x' on another `defface' to
override the previous definition, but how can you do that programmatically
(without resorting to `eval-defun')?

If there is no good way to do this, how about adding one?