customize-mark-as-set is a compiled Lisp function in `custom.el'.

(customize-mark-as-set SYMBOL)

Mark current value of SYMBOL as being set from customize.

If the default value of SYMBOL is different from the saved value if any,
or else if it is different from the standard value, set the
`customized-value' property to a list whose car evaluates to the
default value. Otherwise, set it to nil.

Return non-nil if the `customized-value' property actually changed.