You should only have to modify your code to this:
function change_mce_options( $init ) {
$init['theme_advanced_blockformats'] = 'p,address,pre,code,h3,h4,h5,h6';
$init['theme_advanced_disable'] = 'forecolor';
$init['paste_remove_spans'] = true;
return $init;
}
add_filter('tiny_mce_before_init', 'change_mce_options');
Also, make sure so your cache is cleared by disabling/re-enabling your theme or plugin.