Url rewrite changes not taking effect

I’ve got WordPress installed on XAMPP on my local system and I’m stuck on a problem with url rewrites. I’ve changed the permalink settings to http://localhost/wordpress/%postname%/ and that works fine. But I’ve edited post.php so that the page name is prefixed with the post ID (mainly to replace the -2 slug suffix that appeared when two posts have the same name), so urls now appear as www.mysite/wordpress/somecategory/117_here-is-a-post and /118_this-is-another-post

I’d like to rewrite the url so the the post ID doesn’t appear, but none of the changes I make to /htdocs/.htaccess has any effect.

I’ve checked that AllowOverride All is set in httpd.conf. I’ve made sure that rewrite rules are flushed and apache is restarted with every change I make, and I’ve cleared my browser cache repeatedly. I’ve also made sure that the new rewrites are added above # BEGIN WordPress in the .htaccess file. I haven’t even begun trying to work out the rewrite rules yet, as even the simplest of examples I’ve found online don’t work: nothing alters the urls I’ve edited. Am I missing something?