Yes, it is possible to parametrize a user defined model using an additional infofile. Follow the steps below in order to provide model parameters in an external infofile:

1. In the Vehicle Data Set navigate to the tab that belongs to the model class you want to create an additional infofile for, e.g. Steering, Brake, etc.
2. On the right hand side of the window select "Model > Select save location..." and specify the location and name of your external infofile. The CM file browser offers the possibility to choose between one of the three following save locations: Data/Misc in the project folder, Data/Misc in the installation directory (not recommended) or Data/Misc in a shared data pool in case one exists. 
3. After pressing "Edit" on the right hand side of the window the infofile keys can be specified in the new window.
4. The changes of the additional infofile will be saved every time the vehicle infofile is saved.

In the vehicle infofile the external infofile should be referenced by the key .FName.