To keep it short, is there a way to make an expansion pack, that happens to be bought from Origin, work on The Sims 3 STEAM game with all of it's expansion packs installed? Does said method work that's explained in that forum post? Also, is it possible to uninstall ORIGIN once you get it working?

If that method works, your Origin installation does not play a role anymore. Because you copy the installation to Steam library location and create its own registry entry for that copy. So yes, you could then remove Origin and its games.
You can test this, just be careful with the registry entry you create (make a backup first).
I am very curious to know if it works

Right now I'm trying it out. So along the steps I encouter issues on #8 and #9. So everything was fine until I installed Origin, in which upon logging into it it automatically started downloading TS3 Generations with its detected BG (do note, I didn't bought the base game from that platform)

- The install files, which I suppose should be at OriginGames folder that I'm looking at, is empty. The EP04 file has already settle in the steam directory (common/The Sims 3), which itself seems to be different from the steam-installed expansion packs. Trivial note, though I doubt it makes a difference, I actually moved the Sims 3 document file OUT from the electronic arts (thus making a backup for SAVES) instead of renaming it. Also, maybe I should have when loading up the Origin variation (by launching the game) I should have started A NEW GAME (entering Sunset Valley) instead of instantly quitting after Main Menu, as that theorically I think might have generated more files in the expansion pack's entry folder.
- I can't find (or I'm looking at wrong location) where are the registry systems of all games, both from steam and Origin (well, kinda, the one I found is this one:
- Also, the expansion pack of the Origin game that I'm trying to transfer over Steam platform (so-to-speak) is differers being the latest (1.69) than the Steam one (1.67). But I suppose and REALLY hoping installing the patch that's provided by MTS succesfully downgrades it. ETA: didn't work, as appearantly it couldn't detect any other versions, which could mean didn't recognize the STEAM's installed The Sims games.

So far, origin is overriding so I only got TS3 and Generations installed, while other packs being unrecognized. Dunno if it was a good idea, but I uninstalled Origin in hopes I can somewhat bypass the incompability for the expansions pack that are cross-platforms. Now I can't seem to launch from either way thanks to me uninstalling Origin Inconviences annoy me when it doesn't go as I planned

Steam downloads have binaries for each expansion and stuff while Origin does not do that. What you are trying to achieve might not be possible because of this.

Registry files are different for Origin and Steam versions. In fact, I had them both installed at the same time once because I wanted to backup 1.69 version of the Store content in case I ever need it in the future. If you separate their user folder, both versions can work if installed on the same PC. Just replace the documents folder for the appropriate version when you want to run the other one.

So it's a hoax

Well I tried it for fun with Katy Perry Sweat Treats. You need to put what Steam version expects in the registry for that specific pack and even then, because there are no binaries, Katy Perry's version is shown as 0.0.0.0 in the launcher (probably looks at skuversion.txt for the version but not sure). I launched the game fine and items were there. I took out the binaries from my latest pack just to test (which is ITF) and when I clicked play, it asked me to insert my DVD of Into the Future. Keep in mind that my base game, ITF and all other packs are all Steam version here except Katy Perry and even after that I got that error when trying to run the game without binaries of the last pack. So that means, because Origin version does not give you binaries, you can only go up to the last DLC you own on Steam.

I still do not recommend this though. I will keep playing with this for now as it is only a stuff pack. It can not really harm my saves that much if something goes wrong and I need to take it out.

Sorry for responding so late, but I have a few questions about what you tried :

What do you mean with binaries? I never installed my Steam TS3 expansions, but any other game as far as I tried in Steam has a standard installation structure? Does EA do something different with a Steam installation (except for location and registry entry) compared to the installation of the Origin version?
It confuses me, because you said that the Katy Perry items were found ingame, which should mean that the Steam TS3 game recognised the installation files.
Is it possible you just need an additional configuration entry (outside of registry) somewhere for the launcher to properly recognise the installation?

Steam version has these folders in a DLC:

Game <-- This is the binaries
GameData
Support <-- Not relevant to game itself so you can ignore this
Thumbnails

Origin version has these folders:

GameData
Thumbnails

In pre 1.69 installations, legit copy validation is done via the last released DLC that is installed. Because of this, when I took out binaries of the ITF just for testing, the game complained about lack of DVDs. I don't know exactly what those binaries do, but they are somehow used to check legitimacy of the game, and provide version info in the launcher for specific expansions not just the base game (which you can't see in 1.69 launcher, for example my version of ITF is 21.0.175.024017). Actual game content is in GameData folder (most of it is here) and Thumbnails folder, which both versions have. And when I installed Origin version of Katy Perry in my Steam installation, it doesn't actually need the binaries because it is not my last pack. Only mimicking registry entries of normal Steam expansions in a way that will work with Katy Perry are enough to make it recognize the DLC and make it work. However this wouldn't work if Katy Perry was the last pack I owned because lack of binaries.

Origin version has a different DRM method which also checks Origin side if you own the expansions or not. I don't actually know this but I know people complaining about Origin server issues and Origin updates affecting the game, which never happens with the Steam version, so I assume it is working that way but who knows honestly?

Oh, right. I misread. I thought you mentioned that Katy Perry worked in Steam version, but still gave an error when launching. Thanks for the elaboration

I bought the last TS3 expansions on Steam, so next time the base game is on sale there, I am going to try this. I don't have that many issues with Origin anymore, but TS3 is the only reason I use it.

Well, all my copies are in digital form, not disks. My last EP is ITF. Will this work?

As you can see in my previous message my installation is not DVD. I did not say my installation is DVD, I said my installation asks for DVD even though it is a Steam install when I take out binaries of the last pack (ITF). My install is completely Steam digital install. So if you have Steam version of ITF, and if you install Origin version of anything before ITF, it can possibly work. I only tried Katy Perry and it worked. If you try to make Origin version of ITF work with Steam it probably won't because it lacks binaries and will probably ask you for DVD. So your latest pack needs to be a Steam install at all times.

@SneakyWingPhoenix, so if your ITF is from Steam, this is worth trying. If your ITF is an Origin version, it might not work because then you will miss the binaries that the Steam version of ITF installs.

@rsanda, are those 'binaries' actually different (new) files? Or just files that are normally located in for example GameData with the Origin installation? I was going to ask for your Steam registry entry for ITF and the configuration files to check this, but I am not sure if this is against forum rules. I just wonder if the configuration files tells the game to look in Game for certain files. Atm I can't test this myself without buying the base game on Steam (which I won't do until it is on sale on Steam).

Your latest released pack should be on Steam. This is not specific to ITF.



https://steamdb.info/app/47890/depots/

Check whatever file information you are looking for for all DLCs and the base game for Steam on here.

For ITF this would be: https://steamdb.info/depot/249180/

It is not that hard to search for what registry looks like on Steam installs:

https://steamcommunity.com/app/4789...943514132091361

These discussions are from way back when Origin and Steam version were relatively similar.

I'm an idiot. I do have TS3 base game on Steam. How else could I have bought the last EPs on Steam? I am going to try this method the moment I am done with my current save.

EDIT : @rsanda I guess you meant with binaries the files in \Game. Like how it was done up to patch 1.67.2, which also let you bypass the launcher if you wanted (this method was removed with 1.69 and the files were just in the parent folder). This confused me, because there are binary files in other folders too. It is not a difference between Steam and Origin, but 1.67.2 and 1.69 installation method.

But like you said, these don't matter except for if the last released EP/SP you own is on Origin and not Steam.

Gonns try this stuff out during a holiday lol.