Hi,
It is possible but it is more complicated than making the cusotm form control to save values into separate fields. This will require to understand how the Form engine works (
webinar video). Or, you can create fully custom form used on the Form tab with custom C# code that will refresh the page and reload the control values according your rules, using AJAX or javascript. then, you will set this ASPX form in the document type properties on the General tab -> Editing Form page setting.
Best regards,
Juraj Ondrus