BuddyPress.org

Check out bp-blogs/bp-blogs-templatetags.php. Those are generally the functions that are called directly in the blog loop.

In your case, you’ll want to filter bp_get_blog_permalink. Something like:
`function my_change_url_function( $permalink ) {
return $permalink . ‘/category/blog’;
}
add_filter( ‘bp_get_blog_permalink’, ‘my_change_url_function’ );`