I created a model in the STAAD.Pro Physical modeler. I am not able to make any changes to the model using the Analytical modeler. The commands in the input command editor cannot be edited either. Can you please let me know why ?

It is not possible to edit models created in the Physical Modeler from within the Analytical Modeler. This is because all assignments in the Physical Modeler are based on physical entities (beams, surfaces etc.) and editing those in the analytical modeler may interfere with those physical assignments which can make the model unworkable. So all edit options for such models are disabled from within the analytical modeler. The design related items are the only ones that you can add for such models from within the analytical modeler because the physical modeler does not handle design as of now and hence there is no interference. If you need to edit a model that has been created in the physical modeler, you would need to do it from within the physical modeler itself. The only way to make modifications to such models through the analytical modeler, is to break the connection with the physical model by going to Utilities > Drop Physical Model from within the analytical modeler. The model would then be editable in the analytical modeler but please be aware that the model would then behave an an independent analytical model. The connection with the physical model would be lost and you would not be able to edit the model in the physical modeler anymore.