I load a package that defines a list of radio stations with defvar
I want to redefine this list after loading the package (I am using
require) because a lot of the stations are defunct.
(setq default-list '((station1) (station99) (stationABC))) ; Redefine.
(add-to-list 'default-list '(station23)) ; Add a station.
Take a look at
Emacs Lisp Intro. See also the Elisp manual, node Setting Variables.
You can also use
setq or your own
defvar before that
defvar in the package is evaluated. That will prevent the package's
defvar from taking effect. See the Elisp manual, node Defining Variables.