Filament stuck in extruder
I had unloaded an ASA filament then loaded a PLA filament. There was a lot of clicking and no purging of the ASA. Cannot remove the nozzle. The PLA has bent and appears to have mushroomed out blocking the nozzle in place. I cannot grip the remaining PLA with pliers to break it out. Any ideas short of dismantling the extruder? 
RE: Filament stuck in extruder
Your nozzle has been clogged because the PLA temperature is not enough to molten the remaining ASA.
You can try to preheat the nozzle to ASA temperature and push back the filament using the needle through the nozzle. Maybe helped by moving the E axis back simultaneously.
Proceed with caution, the nozzle is very hot and the needle can bend easily.
RE: Filament stuck in extruder
When swapping from higher temp filament I load the new one as previous one (e.g. PLA as ASA). And after purge at high temp I load it again as what it really is. That will ensure of proper nozzle cleanup from previous material.
RE:
About an hour of slow and careful work with an Xacto knife got rid of the mushroom cap to let me remove the nozzle. A little time with a heat gun and needle nose pliers got the PLA out of the nozzle's tube. Insert the nozzle and back up the extruder gear and it's good to go. Reloaded PLA as ASA (thanks Biomech and Kachidoki) purged the old ASA remaining in the nozzle and everything is back to normal. A Benchy showed everything is good.