<?php
// register the tag in available tags list
hooks()->addFilter('campaign_template_available_tags_list', function(array $tags = []){
$tags[] = ['tag' => '[FUTURE_DATE_40_DAYS]', 'required' => false];
return $tags;
});
// and parse it
hooks()->addFilter('campaigns_get_common_tags_search_replace', function(array $searchReplace = []) {
$searchReplace['[FUTURE_DATE_40_DAYS]'] = date('Y-m-d', strtotime('+40 days'));
return $searchReplace;
});