Modify the file editor page (action=editfile)

Hello,
I’m new to WordPress and quite new to php too 🙂
I need to show users the date of the last modify of a file.
I don’t need the creation date at all, so my idea is to update the creation date (%file_date%) automatically every time a user modify data (or upload a modified file) through the page ‘/wp-admin/admin.php?page=wpfilebase_files&action=editfile’.
This page always shown the creation date, I just want to use gmdate instead of the original %file_date%.
A screen of what I mean http://i49.tinypic.com/207lxub.jpg

I did my best (or worst … 😉 ) adding this:

if ($action == 'updatefile') {
	$file->file_date = gmdate('Y-m-d H:i:s', file_exists($file->GetLocalPath()) ? filemtime($file->GetLocalPath()) : time())
	}

to line 24 of AdminGuiFiles.php but this doesn’t work at all 😀

Can someone help me?

Best regards

(Sorry for my horrible English :D)

http://wordpress.org/extend/plugins/wp-filebase/