You may need Part 15 for other reasons. IANAL, but just using different antennas may fall under the FCC’s “permissible change” stuff. But imagine Part 15 certification be cheaper than lawyers arguing about FCC rules. 
Ah, yes a test house would want to see a CW/sine/clean carrier for Wi-Fi. I believe Mikrotik uses a special package to enable root access, but they obviously don’t share that. RouterOS certainly does not have CLI to enable CW on Wi-Fi.