How to change the default gnus-message-archive-method?

[romeomedina]

It seems that I don't manage to change at my pleasure
the gnus-message-archive-method variable.
On page 119 of Gnus Manual it is said that I can change the default,
which is:

(nnfolder "archive"
                 (nnfolder-directory "~/Mail/archive")
                 (nnfolder-active-file "~/Mail/archive/active")
                 (nnfolder-get-new-mail nil)
                 (nnfolder-inhibit-expiry t))

, with something like:

(setq gnus-message-archive-method
        '(nnfolder "archive"
                 (nnfolder-inhibit-expiry t)
                 (nnfolder-active-file "~/News/sent-mail/active")
                 (nnfolder-directory "~/News/sent-mail/")))

, but it doesn't work:
I put in my .gnus.el that stuff but the default values did not change.
Please, any thought?

Thanks,
Rodolfo