So for those who do not know, Shared_Skin_Lookup_ID lets an item use a different items marketplace skins, this can be useful when combined with Master Bundle Overrides so we can have “vanilla guns” that support marketplace/stockpile skins and use a new .dat file
here we have a modded ace with a skin on, it will change to any ace skin i currently have equipped just like any other vanilla ace
the only difference with this one is has a different ID, GUID, blueprints, and allowing attachments
Take notes map makers who don’t want to use Unity, this can help spice up your stuff!
Another thing you can do is use it on all new meshes, or modified vanilla meshes (like seen below) im going to show off some I made to give inspiration. To start off here is a scrapped APS
using a Vonya skin. Here you can see I put the skin in blender, its nice to work on the model with a skin applied so you know if it looks half decent (sadly I cannot show you how to get these in blender as some users might use it for theft 
)
DISCLAIMER: NEVER upload mods with marketplace/stockpile skins applied to them YOU WILL GET BANNED, do not import stockpile/marketplace skins into the game as is or on models, you do not own them! this is stealing!, only use Shared_Skin_Lookup_ID to apply skins on mod items for upload or personal use
Just another example for inspiration of a type of Luger carbine, unturned has lots of guns that feel similar,(like the 1911 and luger) so doing something like this can be a blessing for vanilla style map makers who want more varied guns, or a way to add further gun customization options.
now when making these keep in mind you need to have these empties:
Effect: Where the particle effect spawns if the skin has one
Stat_Tracker:where kill counters are put on the item
not entirely sure how “Icon2” works, so sorry to anyone that wants to know 
i assume its necessary though
Icon2: “how skins display in the player’s inventory” (thanks DynaNate)
now an important detail we need to talk about
Skin Details:
Overrides Model
I love this on guns they look so beautiful!, but it is also my bane, hopefully Nelson adds an optional .dat flag that lets Shared_Skin_Lookup_ID be ignored when the skin overrides the model (maybe “Has_Custum_Mesh”… idk) or it triggers fallback skins that work similar to normal skins that resemble the “Overrides Model” skin as close as possible.
Now, currently the only way I know to get around it on “Overrides Model” skins is to make the “new stuff” an attachment, the downside is it can only really be “additive” to the model
Now the Peacemaker does not have a “Overrides Model” skin, but I was paranoid when I made this that the peacemaker might get one, so how this works is it is a vanilla mesh peacemaker with empties moved around, new sounds, the viper reload animation and most importantly for this example, the “adapter” is actually a grip that cannot be taken off.
Last thing to note, as of now if you are making one of these, I would not recommend “new mesh style” mods for these items below as this is a list of every item that has a “Overrides Model” skin, but ill provide what “empty slots” they have just because it may be useful for some creative folk out there (you can use a non “empty slot” its just these slots are essentially “free”)
(some guns have an invisible barrel to suppress it, just make it visible instead for this)
if you should use the barrel slot
if you should use the grip slot
if you should use the tactical
if you should use the sight
if its not a gun, technicaly every slot is free, but not really useful for most stuff
- Cobra
- Heartbreaker
- Bluntforce
- Matamorez
- PDW
- Maplestrike
- Nightraider
- Pool cue
- Ace
- Compound bow
- Military knife
- Picaxe
- Katana
- Pitchfork
- Kitchen knife
- Grizzly
- Zubeknakov
- 1911
- Manchette
- Sledge hammer
- Dragonfang
- Detonator
I also believe all vehicle skins are “mesh overrides” but from what I can tell you cant make mix and match item overrides and vehicle ones
also technically the “free slots” can also be used for completely vanilla guns to be modded in a similar way if you know how to force them on, but that’s a whole different topic, if the restrictions of forcing a vanilla item to have an attachment are not an issue, and the vanilla .dat file of it is fine, you probably should do that instead of my methods.
anyways, go out there and make some cool mods!