When I save a group of clips + their effects and transitions to the library, I notice that it automatically renders them to a single .mlt clip. Is there a way to preserve the group itself? I want to be able to use particular groups between projects, but be able to fine-tune them individually for each project.

when you use it, you can drag it to the timeline with enough space for all the clips and do timeline -> current clip -> expand
it's also at the end of this video : https://www.youtube.com/watch?v=TuDJfDevTxY