If you mean that you want to add some questions to the firstboot inithook config then you'll need to add some files to the inithooks directory of your appliance code as per what the other appliances do (check out overlay/usr/lib/inithooks/ of pretty much any appliance in the library).

If you want to just change the text that confconsole displays then edit /etc/confconsole/services.txt (edit/add it to the overlay if you are building an app from scratch).

Further if you think that your app would be useful for others, is ready for prime time and is open source then please consider releasing it as a TurnKey appliance. I can help you out there if you want...