custom-reevaluate-setting is a compiled Lisp function in `custom.el'.

(custom-reevaluate-setting SYMBOL)

Reset the value of SYMBOL by re-evaluating its saved or standard value.
Use the :set function to do so. This is useful for customizable options
that are defined before their standard value can really be computed.
E.g. dumped variables whose default depends on run-time information.