Give your Query a unique ID to be able and filter it in the server side using add_filter() function.
This is how you do it:
//modify the arguments here.
//widget data is an array with all widget settings
function modifyMyQuery($args, $widgetData){
return($args);
}
add_filter("my_query_additions", "modifyMyQuery",10,2);
Note that $args variable is array of query arguments and not “query” object.
$widgetData is an key / value array of all widget options