How can I programmatically change the parse mode?
On Drupal 7, I've achieved this by using hook_views_pre_build() since this hook is executed before hook_views_pre_execute() and hook_search_api_views_query_alter(). Using code similar to the following will do the job.
$options = $view-&gt;display_handler-&gt;get_option('query');
$options['options']['parse_mode'] = 'TYPE_OF_PARSE_MODE';
$view-&gt;display_handler-&gt;set_option('query', $options);

Note that TYPE_OF_PARSE_MODE can be:

Direct query - direct
Single term - single
Multiple terms - terms