There are no files regarding it, a release will be too huge most likely and will not suit all servers. To make models work, you have to recreate the original items (that you want to have models) and create as many copies as models you will have, then @ _refobjcommon you will have to modify their icon's and skin's, this way you will have the base item you want with different icon/skin > model switcher. To make it work "automatically" you will have to create a scroll or whatever (can be bot command) that will trigger a procedure, which does some checks (if item is valid, if there is a valid copy of this item to be replaced, etc..) and at the end you update RefItemID @ _Items with the new one.
If you can't understand ANYTHING from the above text, don't even start on it. You will mess up big time.
