I have 3 models in my resource pack for block models. One is "block_6_model", which defines the elements the model should use. It refers to each texture using the file location. Here is the relevant portion of "block_6_model":

{
    "textures":{
         "stud": "plasticraft/colors/blue",
         "particle": "plasticraft/colors/red",
         "top": "plasticraft/colors/red"
     },
    "elements": [(omitted because of lack of relevancy)]
}

This is meant to be a parent for the model named just "block_6", which then sets the "stud" texture to "top". This way, I can make models that only specify the "top" texture and the "stud" texture will use it as well. Here is "block_6":

{
    "parent": "minecraft:block/.master/block_6_model",
    "textures":{
         "particle": "#top",
         "stud": "#top",
         "top": "plasticraft/colors/red"
     }
}

This works great for blocks where I want to have it use the same texture for "stud" and "top". However, I do not want every model to use the same texture for "stud" and "top". In my "coarse_dirt" model, I set "stud" and "top" to different textures.

{
  "parent": "block/.master/block_6",
  "textures":{
     "top": "plasticraft/colors/reddish_brown",
     "stud": "plasticraft/colors/dark_bluish_gray"
   }
}

Even though it uses "block_6" as its parent, it was still able to change "stud" to a texture unique from "top" before 24w45a. However, in 24w45a, "stud" is set to the same texture as "top" on coarse dirt. Instead of using "dark_bluish_gray" as it did before, "stud" is now set to "reddish_brown".