URL rewriting

Question

Hello,

I know I can rewrite url when application starts. But if I do something before this can I after this change url? I need url rewriting because I find filename by parameters and when I open file in browser, filename is wrong and althought I open it as attachment special characters are not allways right.. I know IE read filename from URL, but I can't use filename straight on URL before I have to use querystring parameters. Can you help with this?

Thank you!