MySQLはユーザーをコピーします

別のテーブルに挿入して列を更新するのはどうですか？次のようなもの：

CREATE TABLE user_tmp LIKE user;
INSERT INTO user_tmp SELECT * FROM user WHERE host ='localhost' AND USER ='root';
UPDATE user_tmp SET user = 'readonlyuser', Insert_priv = 'N', Update_priv = 'N',
    Delete_priv = 'N', /* TODO: ADAPT TO YOUR SUITS */ LIMIT 1;
INSERT INTO user select * FROM user_tmp;
DROP TABLE user_tmp;