These commands allow you to view, modify, add, and delete various bits of information from the info alist. See Information Keys and the Info Alist.
sc-mail-field-query(C-c C-p f)
If you want to modify the value of a key, Supercite will first prompt you (with completion) for the key of the value you want to change. It will then put you in the minibuffer with the key's current value so you can edit the value as you wish. When you hit <RET>, the key's value is changed. Minibuffer history is kept for the values.
If you choose to delete a key-value pair, Supercite will prompt you (with completion) for the key to delete.
If you choose to add a new key-value pair, Supercite firsts prompts you for the key to add. Note that completion is turned on for this prompt, but you can type any key name here, even one that does not yet exist. After entering the key, Supercite prompts you for the key's value. It is not an error to enter a key that already exists, but the new value will override any old value. It will not replace it though; if you subsequently delete the key-value pair, the old value will reappear.
sc-mail-process-headers(C-c C-p g)