You can add objects to a Form List easily enough (via the AddToFormList scripting command) but is there a way to start out from an empty form list, add stuff to it, have things happen in-game, and then have the form list emptied while in-game again for it to be refilled later by a new set of AddToFormList commands?

This would be useful for another reason - if a mod adds something to a formlist via script and that mod is removed, the ID for that object stays in the formlist, even if the object was something created by that mod. So it can leave an invalid entry in your formlist, which breaks some of the FOSE commands (and probably vanilla commands) associated with the formlist. As far as I know though there's no way to empty a formlist or remove items from it short of removing the mod that adds it.

That's what I thought. Just put that down for an NVSE feature request, then (along with a RemoveObjectsByType function that only removes things that are in a formlist rather than everything besides what's in a formlist).

I use that aaaaall the time in FO3- just requires the script extender, with ListRemoveForm/ListRemoveNthForm (E: And the loop functions also, even if RemoveForm was in vanilla it wouldn't be much use in a lot of situations without loops).
Also, RemoveItems Formlist 1 should remove 1 copy of everything in the formlist?

What I'd really want is something that removes all items in a formlist (and all copies of those items), shoves them in a new ref, and maintains those item's conditions, just like RemoveObjectsByType does (but with what the FormList does reversed). This would make, for example, an armor or weapon sorter very easy to set up.

Removing forms from the form list I want so I can make a 'bag' that you can carry around and have all the items you loot get thrown into that, but keep all the items you already have out stay where they are. That way I won't get bogged down in the loot I'm picking up and finding all the useful items I'm carrying will be easier. Maybe different bags for different types of items (like one for books/magazines, one for crafting items, one for chems, etc), though just making it so I can just have the objects I already got in my inventory in my inventory would be great.

EDIT: And yeah, I knew you could remove items from a formlist with the script extender, but I was hoping there'd be some way to do it without it, since the extender isn't released yet for NV and probably won't be for a while.