Hi Nick.
I hope others answer here, and if/when my project gets going, I’ll be sure to publish.
Based on your message, I think yes: you will need to write specific client and Lambda functions for each aspect of user interaction. In the case you describe, the pair of functions might be a client function that sends a message with one of a few different input values (like from a drop down menu) and the Lambda might be a ‘write this value’ function that changes the data store. Mike’s example provides both sides.
I don’t know enough about JavaScript or Lambda to write these sorts of things, and so I am asking for expert help. But I don’t imagine there’s too much more than writing 2 sides of one request.
Hopefully others can help more, but if you can give more of an example of what you want to achieve, this would probably help people to give you feedback.
Good luck!