The Belair name is well established in the Swiss market since the airline has been active in the charter market for decades (first as Balair, then as Belair). I don't know if it makes sense to change it. Nevertheless, all ZRH based AB planes are in AB livery and carry a sticker next to the door saying "operated by Belair". AB has already reduced the 4T brand appearance to a minimum.

The Belair operating certificate is necessary for flights to destinations outside the European Union, where the EU open skies area does not apply. All flights from ZRH to airports in the EU (Greece, Spain, Italy, etc.) carry the AB code (even if in theory operated by 4T planes in AB livery ). Flights to destinations such as Pristina, Sharm-el-Sheikh, Hurgada, Antalya carry the 4T code since the bilaterals between Switzerland and these countries require a Swiss company to operate the flights. These flights, too, are operated by the same planes in AB livery.

I believe an Austrian subbrand such as NIKI to be necessary for those ex-VIE flights bound for points outside the open skies area.