I have a website on a shared server (apache), one of my scripts needs the exec function to work, but my web host seems to have disabled it..is there any way to enable it thr
No, there isn't. That is a php internal setting, whilst .htaccess only deals with apache internal request handling.
And by the way: since this is apparently a hosted site you are using: there are very good reasons to disable that feature. It would be a massive security problem for a web space hoster.