Streamline usage of --eff flag? #107
Description
Currently, the --eff flag requires the user to supply an entirely new template. This is a little unwieldy, and requires going into the source code and copying the weird f-string eff template. Having this option for flexibility is nice, but there could be a simpler use case.
If the goal is just to add a new chunk of code to the eff file, then the user could alternatively supply just that addition, through a new e.g. --eff-append flag.
The issue with this approach is that the eff file has some sophisticated nesting, and parameters have to go in the correct level of that hierarchy. Perhaps implementing this will require treating the eff file as a JSON-like structure (which it is!).