repackage an rpm from an installed rpm

On linux can we repackage a installed rpm if so how.I remember that the a rpm can be generated from the installed binaries

  rpm -??? > my.rpm

Also the later i.e, the newer rpm should work on a different machine

Can you create an RPM from an installed package?

Rpmerizor is a script that allows you to create an RPM package from installed files. You simply have to specify files on the command line and answering a few interactive questions to fill rpm meta-data (package name, version ...). You can also use it in batch mode with command line options for meta-data.

There is also rpmrebuild http://rpmrebuild.sourceforge.net