probably the most efficient way to add parameters to models that were created without them is to use Modelcheck. You can set the configuration to automatically add any parameters you want. You list them in the init file for modelcheck and away you go. You can run modelcheck in batch mode on a whole directory of models and do them all. Modelcheck is not the easiest program to set up. Ther are 3 or 4 files that need to be editted to work well but if all you want to do is add parameters then this would be relatively easy.
My suggestion however is to add them all to your start part with values like TBD so they are always there. And send them to your vendors for them to use as well.