Question about Origin Access and Sims Packs

Good guess on how it works @DaWaterRat, and @Felicity1169 explained it perfectly! The 10% discount is applied to purchases while you are an Origin Access member. If your membership expires, the purchases you made will still be in your Origin Game Library and you can keep playing as usual. Basically, it works as if you purchased a game during sales. :)
However, games from The Vault that you added to your Game Library for free during your Origin Access membership (this includes Deluxe upgrades or packs) won't be accessible anymore if your membership expires.