It is possible to "upgrade" the SDK from the RHEL5 Developer to the RHEL5 Product version simply by downloading the ISO image for RHEL5 Product from Passport Advantage® and accepting the license.
# ./cellsdk --iso /tmp/cellsdkiso installand accept the IPLA license when it is displayed. The rest of the installation process is similar to before. Because the content of the two ISOs is exactly the same, this second install will not install any additional RPMs unless explicitly selected in the Pirut GUI.