Reinstalling a package in Debian isn't too hard (read the man page). However, for those that Google instead of manpage, this is a quick couple notes on some helpful reinstall points.
First, to reinstall a package, issue the following:
apt-get --reinstall install <package-name>
Now, if you're working through reinstalling a specific package that's related to your build then it might be helpful to remember that you can pass variables to this. Such as for reinstalling bits and pieces of the kernel.
apt-get --reinstall install linux-image-$(uname -r)