custom-view-slugs.php

add_filter( 'tribe_events_rewrite_rules', 'rename_event_view_slugs', 10, 2 );

function rename_event_view_slugs( $rules, $new_rules = null ) {
	if ( null === $new_rules ) return $rules;

	// Original event view slugs and what we want to change each to
	$to_change = array(
		'list'  => 'all-events',
		'month' => 'calendar'
	);

	// Scan for rules relating to the views in question and update accordingly
	foreach ( $new_rules as $added_rule => $query_string ) {
		foreach ( $to_change as $look_for => $change_to ) {
			// Skip if we don't have a match
			if ( false === strpos( $added_rule, "/$look_for" ) ) continue;

			// Form the revised rule
			$revised_rule = array(
				str_replace( "/$look_for", "/$change_to", $added_rule ) => $query_string
			);

			// Remove the old rule and insert the new one
			unset( $rules[$added_rule] );
			$rules = $revised_rule + $rules;
		}
	}

	return $rules;
}