No. You can only use our officially released plug-ins with MixEmergency. It is possible to make a Quartz Composition overlay that acts like a transition, but it will not behave like regular transitions (i.e. it won't be in the transition list, you can't trigger it via preset, etc). Also, most of these Quartz Composition overlay "transitions" will not perform quite as well as our optimised plug-ins.
