A Passphrase Problem

[Victor Stuart]

Hi all,
    I'm a newbie, and have some problems with the software. I
generated a pair of keys, and set the password for the secret key.
Then I just noticed the option "--passphrase-file" in the manual, and
quite appreciated that. I wanted to use a file as a passphrase,
instead of a string. So I just did this: I edited the key, erased the
original passphrase, and then typed "gpg --passphrase-file xxx --edit
xxx"
Command>passwd
    Finally I changed the passphrase to the file xxx successfully. But
just then I found a serious problem, how can I change the passphrase?
I tried to use the option "--passphrase-file " again but it didn't
work. Original passphrase-file needed before I could change it. I am
puzzling   #_#    Do you have any idea to help me change it back or,
must revoke it?

Victor Stuart