I have a set of product pages that obey the following htaccess rule:
RewriteCond %{REQUEST_FILENAME} !-s RewriteCond %{REQUEST_URI} ^/([0-9]+)\\-(.+)\\.html
Your looking for QSA, Query String Append
RewriteCond %{REQUEST_FILENAME} !-s RewriteCond %{REQUEST_URI} ^/([0-9]+)\-(.+)\.html RewriteRule ^(.*)$ /product/index.php?prod=%1-%2 [L,QSA]