There is, but it's not friendly - yet. We are working on UI to allow for easy reversion back to an inherited state, as well as clearly defining which areas are being overridden.
You can manually delete the C:\Program Files\Inductive Automation\Ignition\data\projects\projectName\ignition\event-script\data.bin (Windows) file. After a short amount of time the Designer should receive information that the resource has been removed and the next time you update the project (File > Update Project, or try to Save), the Gateway Events should be back to its original inherited state.
100% expected. The project is not runnable, so will not ever go through the startup process.
I'm not sure what tag setup you're performing, but it seems like that might best be handled by the Child projects as part of their startup.