Can anyone please tell me if it is possible to add a new custom tab to the Toolspace within Civil 3D. If it is, could you please demonstrate how this is done.
As far as I know, the Toolspace has not been exposed in any API. I thought there was a post from one of the Autodesk guys a few years ago about this, but I cannot locate it just now.
At the AeccUiMgd.dll assembly there is a class Autodesk.Civil.AeccUiMgd.Toolspace, that inherits from Autodesk.Civil.AeccUiMgd.PaletteSet, which is not the same as the AutoCAD and don't have the methods we need to fully manipulate.
So that is why this is not possible, sorry.
Autodesk Developer Network