I was thinking something more like how you would find the masterworks spyglass in the lighthouse, that sort of pickup based way of acquiring items. So you got a little box pop up saying "you have found x" and options to "take or leave". So as if it were a new item, but instead of it being added to you inventory and having to "equip" it as such, it just appears in the page where you choose your outfit. However your original reply to my idea was implying it was a similar system to other stories where it auto equips the clothes, but doesn't give you a direct option to choose what to wear.
There are several ways to do this, listed here in order of complexity:
1. As suggested by me in post #2: Quest case gets executed, you immediately get the new outfit applied to your player character
Advantage: Requires just a single line of code.
Disadvantage: The player gets no choice and, as
@Jack Rackham rightly points out, looks a little strange.
2. As suggested by me in post #4: Quest case gets executed, you get the outfit added to your inventory along with an on-screen (LogIt) message,
but it does NOT get automatically applied to your player character. You can do that manually through the interface that already exists.
Advantage: Requires just two lines of code and the player does get the choice.
Disadvantage: May not be very obvious when it happens; an on-screen message is easily missed.
3. As
@Jack Rackham suggested in post #3: Create separate "pickup" items for each outfit that you want to be available for pickup.
Advantage: You can have custom interface pictures and item descriptions for them.
Disadvantage: This is OK for a few models, but will become a pain when you want a lot of different ones.
4. As
@Grey Roger suggested in post #12: Place a "generic outfit pickup item" that you can take or leave and that gets swapped out with the actual outfit if you decide to pick it up
What outfit you get could be determined by "current location", a quest-based character attribute or maybe some method I didn't think of yet.
Advantage: This solution should work for any and all character models in one go. Plus you don't get the item permanently in your inventory, so it doesn't matter if you get a lot of them.
Disadvantage: Interface picture would by necessity have to be a generic one. Using preprocessors, we
may be able to correctly update the item description though.
All options are possible. #1 and #2 you could probably do yourself without anyone's help.
The other two require more work, so if that is what you want, hopefully somebody is willing to support you with it.