Hi,
if you use "Advanced configuration" then the window is not modal => you do not need to close it, you can save the changes and enforce your settings.
You can also open the
https://NAC-GW/screen_preview and see how all those web pages looks like => you do not need to go through the registration process.
I saw some plans to improve the captive portal design on the roadmap => our development is aware of this and will make it more EASY in the (near) future. (of course subject to change without notice)
I have seen a lot of heavily customized captive portals with our NAC...
good luck!
Zdenek
Regards
Zdeněk Pala