Cara, isso se chama query.
Para deletar TODOS os players, menos os Acc Man e os Samples, execute essa:
DELETE FROM `players` WHERE NOT `players`.`name` IN ("Account Manager", "Rook Sample", "Sorcerer Sample", "Druid Sample", "Paladin Sample", "Knight Sample");
Se você quiser usar a sua query:
DELETE FROM players WHERE level < 50 AND lastlogin < UNIX_TIMESTAMP() - 20*24*60*60
Como voce mesmo disse, isso pode fazer com que os samples e o Acc Man sejam deletados.
Se forem deletados, basta você executar essa:
INSERT INTO `players` (`id`, `name`, `world_id`, `group_id`, `account_id`, `level`, `vocation`, `health`, `healthmax`, `experience`, `lookbody`, `lookfeet`, `lookhead`, `looklegs`, `looktype`, `lookaddons`, `maglevel`, `mana`, `manamax`, `manaspent`, `soul`, `town_id`, `posx`, `posy`, `posz`, `conditions`, `cap`, `sex`, `lastlogin`, `lastip`, `save`, `skull`, `skulltime`, `rank_id`, `guildnick`, `lastlogout`, `blessings`, `balance`, `stamina`, `direction`, `loss_experience`, `loss_mana`, `loss_skills`, `loss_containers`, `loss_items`, `premend`, `online`, `marriage`, `promotion`, `deleted`, `description`, `created`, `nick_verify`, `old_name`, `hide_char`, `worldtransfer`, `comment`, `show_outfit`, `show_eq`, `show_bars`, `show_skills`, `show_quests`) VALUES
(1, 'Rook Sample', 0, 1, 1, 1, 0, 150, 150, 0, 0, 0, 0, 0, 110, 0, 0, 0, 0, 0, 0, 0, 50, 50, 7, '', 400, 0, 0, 0, 0, 0, 0, 0, '', 0, 0, 0, 201660000, 0, 100, 100, 100, 100, 100, 0, 0, 0, 0, 0, '', 0, 0, '', 1, 0, '', 1, 1, 1, 1, 1),
(2, 'Sorcerer Sample', 0, 1, 1, 8, 1, 185, 185, 0, 0, 0, 0, 0, 128, 0, 0, 35, 35, 0, 0, 2, 0, 0, 0, '', 600, 0, 0, 0, 0, 0, 0, 0, '', 0, 0, 0, 201660000, 0, 100, 100, 100, 100, 100, 0, 0, 0, 0, 0, '', 0, 0, '', 1, 0, '', 1, 1, 1, 1, 1),
(3, 'Druid Sample', 0, 1, 1, 8, 2, 185, 185, 0, 0, 0, 0, 0, 128, 0, 0, 35, 35, 0, 0, 2, 0, 0, 0, '', 600, 0, 1302858859, 16777343, 0, 0, 0, 0, '', 0, 0, 0, 201660000, 0, 100, 100, 100, 100, 100, 0, 0, 0, 0, 0, '', 0, 0, '', 1, 0, '', 1, 1, 1, 1, 1),
(4, 'Paladin Sample', 0, 1, 1, 8, 3, 185, 185, 0, 0, 0, 0, 0, 128, 0, 0, 35, 35, 0, 0, 2, 0, 0, 0, '', 600, 0, 0, 0, 0, 0, 0, 0, '', 0, 0, 0, 201660000, 0, 100, 100, 100, 100, 100, 0, 0, 0, 0, 0, '', 0, 0, '', 1, 0, '', 1, 1, 1, 1, 1),
(5, 'Knight Sample', 0, 1, 1, 8, 4, 185, 185, 0, 0, 0, 0, 0, 128, 0, 0, 35, 35, 0, 0, 2, 0, 0, 0, '', 600, 0, 0, 0, 0, 0, 0, 0, '', 0, 0, 0, 201660000, 0, 100, 100, 100, 100, 100, 0, 0, 0, 0, 0, '', 0, 0, '', 1, 0, '', 1, 1, 1, 1, 1);
Espero que sirva pra algo...