I changed file htaccess in your instructions as following, but error occurred.
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]
# BEGIN Hide My WP
RewriteRule ^other/js/embed\.min\.js /wp-includes/js/wp-embed.min.js?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^other/(.*) /wp-includes/$1?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^file/(.*) /wp-content/uploads/$1?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^ext/(.*) /wp-content/plugins/$1?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^skin/([_0-9a-zA-Z-]+)/main\.css /index.php?style_wrapper=true&template_wrapper=$1&ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^skin/([_0-9a-zA-Z-]+)/style\.css /nothing_404_404?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^skin/(.*) /wp-content/themes/$1?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^ajax /wp-admin/admin-ajax.php?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^inc/(.*) /wp-content/$1?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^(readme\.html|license\.txt|wp-content/debug\.log|wp-includes/$) /nothing_404_404?ddd_hide_my_wp=1234 [QSA,L]
RewriteRule ^(((wp-content|wp-includes)/([A-Za-z0-9\-\_\/]*))|(wp-admin/(!network\/?)([A-Za-z0-9\-\_\/]+)))(\.txt|/)$ /nothing_404_404?ddd_hide_my_wp=1234 [QSA,L]
# END Hide My WP
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
</IfModule>
# END WordPress
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