I have to agree geophil, the world origin height is a puzzle. It seems to set a reference level but doesn't actually change any height data in the map - the get height tool in surveyor measures height with respect to the world origin if it's set but the apply height tool doesn't - so much for consistency.
If you have a new baseboard and set a world origin with a 0 height then raise the ground to 100m the heights will read 100. Edit the world origin elevation and set it to -100 and the heights now read 0m. But merge a baseboard with 0 height and the two are still 100m difference in height - the new one attached will read -100m and the old one 0m. So for actually changing heights it's useless.
Bob Pearson