How do you Add/Remove design layers

Have you tried the Layer Stack Manager under the Home tab on the PCB editor? This gives you the ability to add, delete and rename layers although I haven't tested this on an imported design.

I don't think the layer Stack Manager will solve this problem because I believe the layer Stack Manager is just for editing the physical layers.  What I am talking about are the design layers, such as "Top Layer", "Assembly Text Top", "Outline", "3D Top", etc.

The design layers are used to create the physical layers depending on how you set up the build properties.

The mechanical layers can be renamed by bringing up the "View Configurations" dialog (e.g. right click layer tab > Layer Colours...). Click once on the layer name to highlight it, press F2 to enter edit mode which allows the layer to be renamed. An alternative to F2 is to click again on the name text but make sure this is a second click rather than double click action.

I had also seen that I can rename layers like you say, but this dialog doesn't seem to allow for adding/deleting layers.  It seems you should also be able to add/delete layers, but I haven't figured out how.  Any help/suggestions on that?

I don't believe it is possible to add or remove mechanical layers. One option would be to disable the unwanted layers using the Enable box. If you deselect "Only show enabled mechanical layers" it should show the unused spare mechanical layers, one on which you can enable and rename to "Outline".

I think Peter Barnard was close.  In addition, try using the view configurations function. Left click on the color box for the layer selections to open View Configurations.

In the mechanical layers section, untick the Enable box.

If there are primitives from components on that layer then it shouldn't delete.  However, if it is something like a mechanical layer only (like say, imported DXF) then it should ask if you want to delete.

You can test this by enabling an unused mechanical layer, drawing something there and then attempting to un-enable it.

Hope this helps.

Added: alternative ways to open the View Configurations window are:

1) right-click on the PCB design space, click Options, then click mechanical layers or Board Layers and Colors.

2) right-click on the layer tab then left click on Layer Colors.

3) easiest is to single left click on the color box near the LS text. In AD the LS box would bring up your saved layer views but that doesn't work in CS.

Layer Colors in #2 above and Layer Colors in #1 (Options) are not the same and it is part of the learning curve of finding your way around AD and CircuitStudio.

The OP asked about how to add a layer; until the Only show enable mechanical layers box and then tick the Enable and Show boxes on an unused layer.

To rename a mechanical layer, highlight the layer name with a left click. Then left click again.  You can left click a third time to get the editor cursor for single character changes.