It would be great to have a special string for autotext and templates: %LINE_NO% that would display the current line Number of the cursor. In fact, the best would be to be able to customize the list of special strings...
Our code to expand Autotext and Code Templates looks for special strings and expands them as we have instructed. The behavior is similar to a compiler looking for reserved words.
You cannot create your own special strings for us, just as you cannot create reserved words in a compiler (and expect the compiler to do something with them.)
That said, we can consider your LINE_NO request.
We have grand plans to revamp our language for Autotext and Code Templates. Sometime this year.