You should keep the name the same, otherwise you have to link the new soldiers to a squad and then to a building.
From the tutorial:
If you don't change the name of the unit while cloning it, the original unit which is being cloned will be overridden by this clone. This allows you to edit existing units.
However, if you choose to change the name of the unit, a new unit will be created instead.
I'll just ask some basic questions to be sure, because all your steps seem right.
- Does the build succeed? Can you verify the modified date of the .sga files?
- Have you selected the right tuningpack in the custom gameoptions? and do you use a custom win condition at the same time?