I would like to know if it's possible to programmatically access information from the yun board, about SNR/signal strength of all devices connected to it when it is in access point/router mode, and how to go about this.
Use pretty-wifi-info.lua as template:
Got that info by writing a python script that sends a get request to this url:
assuming of course your username and password for the advanced web panel configuration page are root and arduino respectively. you can run this file on your own computer while connected to the yun's network, or you can transfer the file to your yun and run it on that if you see fit. For file transfer If you're using a windows machine, use winscp (WinSCP :: Official Site :: Download) since windows does not have a native scp/secure copy package. otherwise call scp on your command line and you should be good. Then run by SSH-ing into your arduino yun (for windows use puTTY http://www.putty.org/) and calling python