You should be able to disconnect using Apple script.
Also, I think there is a possibility to toggle WiFi on/off in the BTT actions, but I'm not sure about it.
use framework "CoreWLan"
current application's CWWiFiClient's ¬
sharedWiFiClient()'s ¬
interface()'s disassociate()
use framework "CoreWLan"
tell the current application's CWWiFiClient's ¬
sharedWiFiClient()'s interface() to ¬
setPower:(not powerOn()) |error|:(missing value)