How to apply vertical offset to point cloud or project

I need to offset point cloud / project elevations so that my project aligns vertically with an adjoining project that uses a different vertical datum.
I tried "select output coordinate system / advanced / geoid height above ellipsoid " and entered the offset I wanted. After processing the point cloud everything looks the same. I am using GCPs so perhaps that is constraining the offset. Or maybe I need to restart the project from initial processing.
Any ideas on how to adjust a project to a different elevation?

Hi there. Did you reoptimize after updating the vertical CS info? This is necessary for the changes to take effect.