When you throw a costume party, guests change into random costume outfits selected from a pre-made outfit list. I’ll show how you can add your own outfits to this list.

Required Programs:

• S3PE
• SimOutfitter
• S3OC (Optional)
• CTU (Optional)

Pro Steps:
1) Copy the “TrickOrTreatSituation_0x89121649c768f2d7” XML file into a package. It’s inside the GameplayData.package in the base game folder.
2) Make up unique names for your outfits, add them to the appropriate lists inside the XML file.
3) Create your outfit files using the SimOutfitter tool. Use the unique names you made up before so that you get the correct instance IDs.
4) Import your outfit files into your package. Change their group numbers to “0x78000000”.
5) Save. Load. Done.

Beginner Friendly Steps:
1) Creating tuning package

• Open S3PE. Go to File>Open. Navigate to “*wherever your game is installed*\Electronic Arts\The Sims 3\Game\Bin\Gameplay”. Select “GameplayData.package”. Tick “Open as read-only” so that you don’t make changes accidentally. Click Open.
• At the bottom, there are fields for filtering. Paste “0x89121649C768F2D7” into the Instance field. Tick the box next to Instance field. Click “Set”. Tick the “Filter active” box. Now you should only see the “_XML” resource named “TrickOrTreatSituation_0x89121649c768f2d7”. This is the tuning file we will be overriding. Select that, right-click on it, Export>To package. Give a name to it, let’s call it “MyCostumePartyOutfitMod” for this tutorial. It will save the new package when you click Open.
• We’re done with GameplayData.package, close it.

2) Editing the XML tuning file

• Open your MyCostumePartyOutfitMod.package with S3PE. Right-click the _XML resource, click “Text editor”.
• You will find the lists we want to edit at the bottom of the text file. They are named kChildCostumeNames, kTeenMaleCostumeNames etc. Names are self-explanatory. -(Elders use the adult costumes.)
• Now think of unique names for your outfits. Later, this will help us get unique instance IDs for our outfit files so that they don’t conflict with others. EA’s outfit names go like tmBodyEP8Costume5, afBodyEP8Costume12 etc. Similarly, we can name our outfits in a format like “age-gender-costume-username-number”. That should be unique enough. I will create an adult female outfit for this tutorial and name it “afCostumeSlamyy01”.
• Now add your outfit names in the appropriate lists. I added mine at the beginning of the list; you can add wherever you like but make sure you add the comma and space properly. Add as many as you like, each having a unique name. You can also remove EA’s outfits from the lists.
• Save the text file. When you close the text editor, S3PE will ask if you want to commit the changes, say Yes. Save your package.

3) Gathering clothing packages
We want to add clothing parts to our outfit like shoes, top, hair etc. If you want a custom clothing piece, just copy the CC package file. If you want to use an EA clothing do this:

• Open S3OC. At the top, go to Cloning>CAS Part.
• Now find and select the clothing item you want from the list. The list is huge but you can click on the column labels at the top to sort by name and expansions to make it easier to find stuff. -(Also, if you use MasterController, while creating a sim, you can right-click on a clothing thumbnail, which shows its info and exports it into a file so that you can find it easier in S3OC.)
• At the right bottom corner, click “Clone or Fix”. The options show up. Untick “Deep clone”. Definitely untick “Renumber/rename internally”!!! You can enable compression and include thumbnails, doesn’t matter. Click Start. Save the package, name doesn’t matter.
• After you clone all the stuff you like, close S3OC, we’re done here.

4) Editing the design presets
To change the colors/patterns of a clothing part, we will use CTU. If you’re using a CC clothing, make sure to edit the copy, not the original.

• Open CTU. File>Open, select one of the clothing packages you gathered in Step 3.
• Go to “Designs” tab. Select one of the numbered designs. Under that, select the “Patterns” tab. Again, under that, there is “Patterns:” with the options “Pattern A,B,C,D”. Those represent the 4 main coloring channels you see in Create a Style in game. Not all 4 of them are available for every clothing. Select and edit each.
• If you want plain color, select “Solid Color” from "Type".
• If you want to use a pattern, click “Browse Patterns” button. If you chose a multi-color pattern, select “Pattern (Coloured)” from “Type”. "Pattern (HSV)" is for single color patterns.
• To change colors, at the bottom, there are color boxes, click on them to open the Color Picker window.
• When you’re done editing, go to File>Save. We’re done with CTU.

5) Exporting CASP files
Now we need to export the CASP files from the clothing packages.

• Open a clothing package with S3PE. Select the resource with the “CASP” tag. Right-click, Export>To file. Save without changing its name! Repeat for all clothing you gathered. -(Alternatively, you can merge all of them, then select and export all the CASP resources at once.)
• They are exported with “.caspart” extension.
• Now that we took the organs CAS parts of the clothing packages, they are useless, you can get rid of the packages if you like.

6) Creating the outfit files

• Open SimOutfitter. Go to File>New outfit (or “Open outfit file” if you want to edit an existing one).
• Important: In the outfit name field, you should paste your unique outfit name exactly as the way you wrote in the XML file in Step 2. This gives the outfit file an instance ID based on that name and that’s how the game will recognize your outfit. Mine was “afCostumeSlamyy01”.
• Make the appropriate age and gender selections.
• At the top, go to “Add CAS parts>Add from CASP file”. Open a caspart file that you exported in Step 5. If it has multiple design presets, it will ask you to pick one. Repeat and add all the clothing parts you want like this. For this tutorial, I added a CC flame dress by BEO and EA’s firefighter boots to my outfit. You can add other stuff like hair, makeup, accessories too.
• Go to File>Write outfit file. Save without changing its name!
• Repeat this step for all the outfits you want to create.

7) Importing the outfit files

• Open your MyCostumePartyOutfitMod.package in S3PE.
• Go to Resource>Import>From file. Select the outfit files that you created in Step 6. Don’t change anything in the Resource window, click OK. Your imported outfits are tagged “SIMO”.
• Double-click on your SIMO resources to open Resource Details. Change the “Group” number to “0x78000000”. Do this for all of them, otherwise they won’t work.
• Save your package. It’s ready.

8) Finishing
It’s over! Put your MyCostumePartyOutfitMod.package in your Mods folder. Make sure the originals of custom clothing you used are also in your Mods folder. Don’t put the EA clothing you cloned in your Mods. Clear your cache. Test in game
-(Also, I suggest removing most of the EA outfits from the XML file during testing. Otherwise, if you created only one outfit to just test, it will have a very low chance to get randomly selected among all the others and you will be throwing your 37th party trying to just roll that one outfit at 5 am sleepless like me. )


Bonus - Editing Existing EA outfits:

• In the TrickOrTreatSituation XML file, select and copy the name of the outfit you want. I copied "amBodyEP8Costume11".
• Open S3PE, go to Tools>FNV Hash. Paste it in the "Text to hash" field. Click Calculate.
• Copy the result in the "FNV64" field. I got "0xCBD2C70B1A053D2C". Close.
• File>Open, navigate to “*wherever your game is installed*\Electronic Arts\The Sims 3 Seasons\GameData\Shared\Packages”. Select "FullBuild_p16.package". Tick “Open as read-only”. Open.
• At the bottom, paste the FNV64 value that you copied before into the Instance field. Tick the box next to Instance field. Click “Set”. Tick the “Filter active” box.
• Now you see only one SIMO resource. That's the outfit you want. Right-click, Export>To file. Save without changing its name! Close S3PE.
• Open the outfit file in SimOutfitter and edit as you like. Don't write anything in the "Outfit name" field. Export(File>Write outfit file), save without changing its name!
• Open S3PE. File>New. Then go to Resource>Import>From file. In the resource window, don't change anything but you can write the name of the outfit so you will know what it is, just don't click any buttons next to it. Click OK.
• That's it, save the package and put it in your mods folder. This will override the original EA outfit.