Use variable filter names when retrieving your settings

variable-filters.php

/**
 * Set up a global for storing settings in your product
 * (if you're using classes, store it in a controller)
 */
global $myprefix_settings;

/**
 * Set up your own wrapper for accessing settings in 
 * your product
 */
function myprefix_get_setting( $setting ) {

	global $myprefix_settings;

	/**
	 * Get your settings if they haven't been
	 * retrieved yet.
	 */
	if ( empty( $myprefix_settings ) ) {
		$myprefix_settings = get_option( 'mysettings_unique_slug' );
	}

	/**
	 * Filter the setting before returning it
	 * if it's been set
	 */
	if ( !empty( $myprefix_settings[ $setting ] ) ) {
		return apply_filters( 'myprefix-setting-' . $setting, $myprefix_settings[ $setting ] );
	}

	/**
	 * Don't forget to filter it if it's empty
	 * too.
	 */
	return apply_filters( 'myprefix-setting-' . $setting, null );
}

/**
 * Now every time you access your setting, you get a free filter
 */
$the_most_amazing_setting_ever = myprefix_get_setting( 'the_most_amazing_setting_ever' );

/**
 * So when you're writing an addon that needs to modify your
 * setting, you're already good to go.
 */
add_filter( 'myprefix-setting-the_most_amazing_setting_ever', 'myaddon_make_it_better' );
function myaddon_make_it_better( $setting ) {

	$setting .= 'even more amazingness';

	return $setting;
}