The BSSID has to follow HEX characters (e.g. 0-9,A,B,C,D,E,F) "Pickles" does not have valid HEX characters, but "deadbeef" has valid HEX characters. Again, it can be any arbitrary HEX value in the form: aa.bb.cc.dd.ee.ff It does not need to be the MAC address, but most users will make it equal to the WAN MAC address of the AP, so that the BSSID makes sense to a user.

Yes the BSSID can be changed. You can change it via the AP's GUI under Configuration --> Air Interface --> WiMAX Capabilities Or via WM by PMP320AP-->Radio-->Basic Capabilities--> Base Station ID Both can be entered in HEX in the form : aa.bb.cc.dd.ee.ff

Does the BSSID have to be a MAC address?  Are you saying I can't set it to "Pickles"?  If it has to be a MAC, can it be any MAC or should it be the MAC of the wireless interface?