Change the SSID when Yun is in AccessPoint mode is easy; I can edit file /etc/config/wireless or use the advanced web control panel to chenge it.
But if you change from AccessPoint (first configuration) mode to Client mode (normal use) and then yuo return again to the AccessPoint mode (for example, if your wifi is not available or if you're too far away) the name of the Wifi network is again "Arduino Yun - xxxxxxxxxxx".
Change the SSID when Yun is in AccessPoint mode is easy; I can edit file /etc/config/wireless or use the advanced web control panel to chenge it. But if you change from AccessPoint (first configuration) mode to Client mode (normal use) and then yuo return again to the AccessPoint mode (for example, if your wifi is not available or if you're too far away) the name of the Wifi network is again "Arduino Yun - xxxxxxxxxxx".