Hi @torrero007 and thanks for your query. Indeed, the Core SDK does not support individual eye tracking. For this purpose, you will need to use the Tobii Pro SDK which is free to download (https://www.tobiipro.com/product-listing/tobii-pro-sdk/)
However, in order to successfully use the 4C in conjunction with the Pro SDK, you will need to use a special unlock file.
If you have already obtained the analytical use licence, this can be provided for you by speaking with your local sales contact who arrange the licence purchase.
To arrange to use your product for analytical purposes, please be aware that Tobii have now replaced the Analytical Use licence with the Tobii Eye Tracking Data Transparency Policy. You can read more about this change @ https://transparency.tobii.com/
With additional details for developers @ https://developer.tobii.com/license-agreement/
In terms of updating your existing application, I am afraid that the porting to the Pro SDK (which has .NET bindings) involves a different syntax to the Core SDK but hopefully you should not find the transition overly complex.
Please do let me know if I can provide any further information. Best Wishes.