PSpice for TI doesn't have any Model Editing capabilities. You will need to create the model text with a text editor, adding your parameters, and save the text file with a .lib file extension. Then, in PSpice for TI, use PSpice>Edit (New) Simulation Profile, to open the profile editor, and use Configuration FIles, Library and the upper Browse button to Browse to the .lib file just saved, left-click>Add to Design to add this model to the design. Then change the Implementation Property Value of a placed transistor to the name of your model. If you used a sub-circuit, rather than a model, to define your component, you will need to edit the PSpiceTemplate property to map the Pins to an X part, rather than the Q part that the model type uses.