RewriteRule ^blog/[0-9]{4}/[0-9]{2}/[0-9]{2}/(.*)$ /blog/article/$1/? [L,R=301][0-9]{4}- от нуля до 9, 4 раза подряд то есть эквивалент XXXX цифр (.*) любое значение собрали в группу 1$1 - выводим значение 1 группы/? - удаляем гет парметры. - опционально можно не делать
# BEGIN WordPress
RewriteEngine On
RewriteRule ^/blog/[0-9]{4}/[0-9]{2}/[0-9]{3}/(.*)$ /blog/article/$1/? [L,R=301]
RewriteBase /
RewriteRule ^index\.php$ - [L]
# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
# END WordPress
# BEGIN WordPress
RewriteEngine On
RewriteRule ^blog/[0-9]{4}/[0-9]{2}/[0-9]{2}/(.*)$ /blog/article/$1/? [L,R=301]
RewriteBase /
RewriteRule ^index\.php$ - [L]
# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
# END WordPress
RewriteCond %{REQUEST_URI} ! ^blog/[0-9]{4}/[0-9]{2}/[0-9]{2}/(.*)$
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]