Hi,
I'm not sure if I understand it well, but you can modify that with supported Kentico UI. If you create your custom module you can modify it in user interface. The best way to check that is to look into something that's already implemented in kentico. For example, take a look into Page Types application that kentico already have (see image bellow):
Configuration from image above will look like this:
So what you need to do is to create custom module and that custom module need be configured as shown on first image, but you can change page template to use horizontal tabs instead of vertical (depends on your needs). After that, create 3 elements underneath with names:
If each of this tab have custom implementation, then element (for example) called 'Home' can have type: URL and Target URL (instead of page template) will be URL to your custom aspx page: ~/CMSModules/CustomModuleName/UI/Module/CustomPage.aspx
Best regards,
Dragoljub