changing form values on submit

Hi, I have a node form I'd like to change values on when submitted. It looks like there's several copies of the data coming through in $a3 though. Which is the one I can alter and pass along to submit? nid, vid or something else?

I could do this in hook_submit but there's a formatted date at that point and it seems easier to work with the post array, when you're already testing it. Vandyke is saying hook_submit is 'better form' but I think the regex may be a little nicer at this point.