Include OR Group With Exposed Filters in View
I think you can achieve it by adding new filter group from views UI.



Edit:
If your case is more special then you can achieve it using hook_views_query_alter.

if (!$new_feed) { 
  $query-&gt;where[0]['conditions'][1]['field'] = 'node.nid'; 
  $query-&gt;where[0]['conditions'][1]['value'] = array(); 
  $query-&gt;where[0]['conditions'][1]['operator'] = 'IN (' 3, 4 5')'; 
} 
else { 
  $query-&gt;where[2]['conditions'][1]['field'] = 'node.nid'; 
  $query-&gt;where[2]['conditions'][1]['value'] = array(); 
  $query-&gt;where[2]['conditions'][1]['operator'] = 'IN (1, 2, 3); 
}


You can unset where condition as per your use case.