Okay, I had that problem at first too.
This is what you need to do.
1. (Inside data editor) Find the unit you want to copy, and right click on it.
2. Choose "Duplicate Object" and a window pops up.
3. Now check all check boxes in the window that popped up, and click OK. (Now you can change everything about it without modifying the original unit too.)
4. Make sure "Show Object Explorer" is checked by looking in the "View" drop-down list.
5. Select the copied unit, and then select the units actor found inside the Actors folder in the Object Explorer.
6. Now on the right list, look at the very top, and then to the right of "unitName". You should see the name of your unit. Right-click that name and choose Modify Value.
7. Now just find the name of your created unit, probably just the original name with "copy" after. Select it and press OK.
That should do it. ^^