Note that I do not know if this is the best way of doing it and this is something I kinda just made from trail and error.
If you have any pointers on how to do this better let me know!

20 steps to replace any model with another.

Step 1:
Create a new project and select Add-on, also load data from Story and target Story. Set a name for you project and click Create.

Step 2:
When the editor is done loading it will ask you to load a level, this is not needed for this mod so simple press the 'x' or cancel.

Step 3:
I will close down all panels during the tutorial, this is optional.

Step 4:
Open the resource manager by clicking on its icon.

Step 5:
Make sure your mod-folder is selected and press the indicated icon to add an empty package, name it and press ok.

Step 6:
Now to find models open "Shared/Characters/Elves/Elves_Female_Armor"
You should see several items in the list.

Step 7:
You can filter out item-types on this row, for example hiding textures and material resources. This is also optional.

Step 8:
Select what items/models you want to replace. You can use the search bar to find all parts for a particular slot.

Step 9:
When they are selected press "Checkout Current Item".
Press yes on two prompts. Prompt 1 Prompt 2
They should now be present in your package that you made at the start.

Step 10:
Now to find the model you want to replace it with. I will be using the sebille arms.

Step 11:
From this model Copy its Source File location simply by right-clicking and copying to clipboard.

Step 12:
Now go to the model you imported in your package, select it and replace its Source File location.
The item will now look like shit. This is because it got the old textures that does not fit your new model.
Mod item
NOTE: If the Source path is not white and can not be edited then you probably imported it wrong, you must use the Checkout button as mentioned in step 9.

Step 13:
Double-click your item to open the Edit Visual window, here it shows how many and what textures the item uses. Keep this window open.
Now do the same for the item that you wanted to change it into, for me it was the Sebill arms.
Here we can see what the correct texture is named.
correct texture

Step 14:
The correct texture is located in the same place as you found your model, make sure that you can see it and then make sure it is selected.
Now press this button to change what texture to use on the model. button

Step 15:
Repeat this process for all instances that you want to alter then save your project and close the editor.

You are done! Try the mod in-game!

Last edited by Larian_KVN; 03/10/17 04:18 PM. Reason: Forced an update to get the URLs to display correctly.