Not at the UI level. The Broadcom userspace tools (wl and dhd) might possibly allow to adjust that, but you could also do it with the stock firmware. Only difference is if you need to be able to rerun the config commands at boot time, you'd need my firmware to setup boot time commands (or something like OpenWRT).Does your distro really allow control of # of MIMO streams?
I wouldn't know if/how to do it using the userspace tools however, and everyone back in Taiwan who might know the answer is off for the holiday.