The Offset Isometric command is used to stretch part of an isometric diagram without making changes to actual distances or elevations on the plan view.
To offset part of an isometric diagram, go to
Ribbon: DM Plumbing->Isometrics-> 
Offset Isometric
Pulldown Menu: DM Plumbing->Isometrics->Offset Isometric
You will be prompted to identify the isometric pipe to be offset.
Select isometric pipe to offset:
You will then be prompted to identify the location to which the pipe will be offset.
Specify base point:
Specify second point:
The selected pipe will be moved on the isometric diagram. Pipes connected to the selected pipe will be stretched to stay connected.