Bala,
Currently, that is the limitation from modeling perspective. Having said that, I am not sure why you need different template for different lines. Can you throw some light on your use case? This limitation do have some workarounds as below..
For example, if you want to add new properties to all your line, you can implement additional Thing Shape which should make it available to all your line. Same thing with services. On the UI, you may have to expose these properties depending on your case.
If you want to add different properties to different lines, it can be done from the UI as shown below. These properties are at Thing Level.
