We are doing a tract home project and also need to do reverse plans. We only want to have one model to do changes for RFI's, etc. Mirroring the project would create two instances of the model, which would be a pain to manage. Our building official only needs the floor plans mirrored.
So our solution is to create a blank project and link in the original model. Once linked in, mirror the link. Set the plan view to use the original model floor plan view. The dimensions, grids, tags fix themselves in revit. We used a note block for keynotes, these do not mirror, so we will turn them off under the custom view properties. We have done a newer project with standard keynotes, these fix themselves as well!
it depends on the target you want to achieve.
Mirror the project location is for changing the complete project.
workaround by using new file and linking other model is suitable for keeping both the options.
What if you want to have only model with two different orientation.
May be project north/true north can help.... my 2 cents...