Waiting for the HoloLens Emulator's OS to boot up every time I make some changes to my app and I recompile can be annoying. Is there a way to deploy a new build to an already running emulator?
Yes, just don't shut down the emulator. You can push the Stop button in Visual Studio, make your changes in Unity and rebuild. Your open project should detect the changes and ask you to reload the project. Hit the Play button in VS and your new code is redeployed to the emulator.