I just needed to repack a Debian package to solve this problem. After a quick spin to #debian I got this solution:

$ mkdir -p extract/DEBIAN
$ dpkg-deb -x package.deb extract/
$ dpkg-deb -e package.deb extract/DEBIAN
[...do something, e.g. edit the control file...]
$ mkdir build
$ dpkg-deb -b extract/ build/

• -x extracts the package contents
• -e extracts the control files
• -b builds the new package

Done.