events_trickery.php

<?php
/*
Plugin Name: test
*/

function test_filter( $test ) {
	$current_day = intval( date( 'j' ) );

	$change = false;
	$new_array = array();
	$array = explode( ' ', $test );
	foreach ( $array as $key => $obj ) {
		if ( strpos($obj,'tribe-event-day') !== false ) {
			preg_match_all('/\d+/', $obj, $matches);
			$n_pre = $matches[0];
			$n = intval( $n_pre[0] );

			if ( $n < $current_day + 3 ) $change = true;
		}
	}

	if ( $change ) {
		foreach ( $array as $key => $obj ) {
			if ( strpos($obj,'tribe-events-future') !== false || strpos($obj,'tribe-events-present') !== false ) {
				$array[$key] = 'tribes-events-past';
			}
		}
	}

	$final_output = implode( ' ', $array );
	return $final_output;
}

add_filter( 'tribe_events_the_month_day_class', 'test_filter' );