There are functions that destructively change the contents of pairs (lists).
(set-car! pair value)
(set-cdr! pair value)
> (define lst '(a b c)) lst> lst (a b c)
> (set-car! lst 'e) (e b c)
> (set-cdr! (cdr lst) '(or not e b)) (b or not e b)
> lst (e b or not e b)