If I am mod_rewriting a URL from:
http://www.mysite.com/blog/this-is-my-title/1/
to
http://www.mysite.com/blog.php?title=this-is-my-title&id=1
You can add QSA to the RewriteRule flags:
RewriteRule
RewriteRule page_([0-9]+)\.html page.php?id=$1 [QSA]
Will redirect page_1.html?a=2 to page.php?id=1&a=2
page_1.html?a=2
page.php?id=1&a=2
However, be careful because requesting page_1.html?id=2 will redirect to page.php?id=1&id=2, and (in PHP), $_GET['id'] will be 2.
page_1.html?id=2
page.php?id=1&id=2
$_GET['id']