To edit multiple pipes, go to
Ribbon: DM Plumbing->Pipes-> 
Edit Multiple Pipes
Pulldown Menu: DM Plumbing->Pipes->Edit Multiple Pipes
You will be prompted to select the pipes to be edited.
Select pipes to edit:
Edit Multiple Pipes Dialog Box
Changes can be made to the pipes in the same way as when they were inserted. See the Insert Pipe section for more information.