src/Setting/SettingStore.php
public function set($key, $value = null)
    {
        $this->load();
        $this->unsaved = TRUE;

        if (is_array($key)) {
            foreach ($key as $k => $v) {
                Arr::set($this->items, $k, $v);
            }
        }
        else {
            Arr::set($this->items, $key, $value);
        }

        return $this;
    }
public function set($key, $value = null)
    {
        $this->load();
        $this->unsaved = TRUE;

        if (is_array($key)) {
            foreach ($key as $k => $v) {
                Arr::set($this->items, $k, $v);
            }
        }
        else {
            Arr::set($this->items, $key, $value);
        }

        return $this;
    }
Set a specific key to a value in the settings data.

@param string|array $key Key string or associative array of key => value
@param mixed $value Optional only if the first argument is an array