Online ArcGIS resource help provides a list of layer properties which can be used as needed. I am not able to find a way to collapse a layer using ArcPy in it. Please suggest if there is a way to collapse a layer in current data frame.
It may not be a great solution but if you have saved layer files with them collapsed then RemoveLayer followed by InsertLayer sounds like it could do it:
The way a layer appears in the table of contents (TOC) after it is added depends on the source layer and how it appears. For example, some layers are completely collapsed and do not display their symbol(s) in the TOC. This setting is built into the layer. If a layer is collapsed, saved to a layer file, and then added to a map document, the layer will be collapsed in the new map document when added via InsertLayer.
However, my suggestion is that you vote for this ArcGIS Idea.