In case you want to build your configurations on IAP first and then import it to central, there is a feature called template based group. At the time of creating a group, you can set the group mode to template based. At this point, you build config on IAP, then, add it to central and then ask central to fetch config or just copy and paste that config from IAP show running output in to the template text area. This will make the central to use this tempalte config from this point onwards to push to IAP.
If you already have IAP in the group and actively managed by central, as previous posts said, you can un-assign license, then, you get the option to configure IAP from its GUI. You can build your configs, test them , and then add a new group with template mode and then paste IAP config here in this template.
Hope this helps. Its very flexible like airwave in this sense depending on your scenario.
Hope this helps.