The Pipeline Editor can be started in Expert mode only from a command-line prompt.
Caution In standard mode, the Pipeline Editor has built-in safeguards that prevent some actions that could disable a site's pipeline. In Expert mode, these protections do not exist. It is recommended that you do not run the Pipeline Editor in Expert mode unless you specifically need the additional functionality it provides.
If you installed Commerce Server in the default location, you would type the following command:
\Microsoft Site Server\Bin\PipeEditor.exe /e