I'm still stuck though and don't seem to get anywhere with Google. I realize it's probably an easy solution, but I can't find it.
Perhaps if you posted more than snippets...
The function you show outputs the SSID of some network, as a pointer to some memory.
Whether config.ssid is a pointer that you could make point to the same location, or to a different location that you have copied the data that BSSID points to, or is an array or is something else entirely, is not at all obvious.
So, how to get the BSSID value into config.ssid remains a mystery. That mystery COULD be solved easily if you posted links to, or better descriptions of, the libraries you are using - links to non-standard libraries; better descriptions of libraries included with the IDE.