ScratchList or some such thing

I have an EventList with a bunch of data relative to many files. API consumers can ask for a pared down list  that contains a list of elements that only pertain to a particular file on disk. Here's the simple pipeline:

EventList (all data) -> FilterList (data for a given file)

My problem is this:

The consumer of that list wants to render the list contents on screen. They also want to allow the user to edit the contents of that list without actually committing the changes upstream yet (so the list would be in a "dirty" state).

Is there any solution built in to GL for such a problem? Do I need a new type of list, like a ScratchList that can be used to locally edit and then push it's changes upstream? Am I thinking about the problem wrong?

Thanks guys!
-Ken