For any resource pack creator seeing this, you probably saw the resource pack changes in last week's snapshot
If you haven't, there was a big change in Item Model Definition. Now you define what model the item will use in a folder in the resourcepack called "item".
There are several ways to change this, but one got my attention in particular: select property custom_model_data. With the right setup, this will change the items model depending on its custom model data.
If you can specify what model an item uses by the custom_model_data component, why not do the same for custom_name? This is CIT in Vanilla Minecraft!