HI,
This can be achieved in two different ways,
1. Create a new SSID profile and map to a new VAP profile along with a AAA profile, create a new AP-Group and map the VAP profile to it ( If you want you can add other VAP profiles from the existing AP-Group). now select AP Installation and select the specific AP which you want to have this and provision with this new AP-Group
2. Select Configuration-->AP specific-->create a new VAP along with the existing VAPs or exclude any from existing VAPs , that's all
Second method is more handy method,
For your ref :
Please feel free for any further clarity on this.