The title is a bit vague, sorry. I'm not really sure how to word it concisely.

I have a computer running Windows 10 that I want to install Sims 3 on, but it uses Origin. Most of my game codes redeemed just fine, but there are two (World Adventures and Ambitions) that I bought secondhand that were evidently already redeemed under another account. I know these codes are operational because I've installed them on my Mac (which doesn't use Origin) and they're fully functional there. I just can't redeem my games through Origin on the Windows.

Because I already have all my other Sims 3 games installed through Origin, I know installing it through the CD without any adjustments won't route it to the correct installation path and will probably bork my existing installations. However, let's say I were to take the CD and install it that way, but instead reroute the installation to where I have Origin Games > The Sims 3 installed. Would that work, or would I just damage my current install files that way? And if so, is there some other way I can install these files that doesn't involve breaking things or repurchasing the game?

(For what it's worth, I already made the mistake of contacting EA Support and asking if there's some way of doing this, but I just kept getting the runaround of "we can't help you, you'll have to repurchase the games", which I can't afford to do right now. At least if MTS says "you can't do this, you have to rebuy them", I can trust that you guys actually know what you're talking about...!)

Origin is set up to manage mixed disc/download installs by way of Patch 1.69. It doesn't matter where the executable files for the EPs end up, under Origin Games or EA Games, the Origin client is supposed to recognize, handle, and potentially reorganize them as it wishes. In reality though, it doesn't do a very good job with the mixed installs and many players find that they have to switch to all one or the other, usually in favor of Origin downloads.

With discs though that cannot be registered because they had a prior owner and their codes have been used by another party, I'm afraid there really isn't any recourse here. EA's stance is that you do not own a license to run those EPs as such licenses are not transferable and you would have to purchase them anew from an authorized retail source to get them recognized by Origin as part of the game it will then allow you to play.

If it's any help at all, the entire collection usually goes on sale at Steam a few times per year for something like 70-80% off. You would have to purchase the base game from Steam (again) in order to purchase any EPs, it won't allow the sale otherwise, but they do throw in Origin codes for such purchases at no extra charge. Thus for the otherwise unneeded base game and two EPs, the total price tag might be as low as $15 USD or even lower while a sale is going on. Plus you get 1,000 TS3 Store points for each of the base game and WA, a very old offer that is still being honored. The game and its packs do occasionally go on sale by way of Origin, but not nearly as often and not usually at such a high discount.