The controller has to call restartComponent(kLatencyChanged), you can send a message from the processor to the controller.
1- processor → send to controller a message
2- Controller gets the message → controller call restartComponent(kLatencyChanged)
3- host will call processor->setActive (false)
4- host will ask the new latency: processor->getLatencySamples ()
5- host will call processor->setActive (true) (the next process call should handle this new latency)
be sure that your plugin does not change too often its latency 
, the host has to recompute the processing graph for delay compensation, which lead to audio drop.