Used expansions

If you can install the base game via disc, with no Origin involvement, then you can also install packs from your used discs. As long as Origin isn't in the picture, there's nothing to care that your codes have already been used.

To install without Origin, you'd need a base game disc manufactured before September 2012; the later ones require Origin to manage the install process. It seems like some very new pack discs also require Origin, but that's not totally clear, and in any case that's only a recent development, maybe for discs made in the last year or so. Older pack discs should be unaffected.

Sometimes, not all the time but sometimes, people manage to get their packs installed via disc even when those codes have already been used. There's no guarantee that this would work though, and more often it doesn't.