1. Modifier le wp-config.php

2.Renommer les tables

3.Adapter les options de WordPress

update NEWPREFIX_usermeta set meta_key = 'NEWPREFIX_capabilities' where meta_key = 'OLDPREFIX_capabilities';
update NEWPREFIX_usermeta set meta_key = 'NEWPREFIX_user_level' where meta_key = 'OLDPREFIX_user_level';
update NEWPREFIX_usermeta set meta_key = 'NEWPREFIX_autosave_draft_ids' where meta_key = 'OLDPREFIX_autosave_draft_ids';
update NEWPREFIX_options set option_name = 'NEWPREFIX_user_roles' where option_name = 'OLDPREFIX_user_roles';

Ancienne méthode :

/* Modification de la table wp_options */
UPDATE `rmg1234_options`
SET `option_name` = REPLACE( option_name, 'wp_', 'rmg1234_' )
WHERE `option_name` LIKE 'wp_%';

/* Modification de la table wp_user_meta */
UPDATE `rmg1234_usermeta`
SET `meta_key` = REPLACE( meta_key, 'wp_', 'rmg1234_')
WHERE `meta_key` LIKE 'wp_%';