If you're using default values for everything and you've made some modifications to your policy text file twpol.txt, you can update the policy with:
Code:
tripwire --update-policy --secure-mode low --verbose --cfgfile tw.cfg --site-keyfile site.key twpol.txt
Because it uses
--secure-mode low, make sure you're confident about the box's security since it ignores changes to files made since the last update.
As far as tracking who changed files/directories goes, I don't think you can do it in tripwire - you'll need something else to do that.