I'm making a pallet mockup rendering and some of the packaging designs have changed.
Is there a way to change multiple decals at one time instead of going into each object and replacing the image?
Sorry no each decal is a new copy... you could edit the base image and then replace it as many times as needed but it would not save any time because you would still need to place them one at a time.
Here is workaround that can help in this situation. You can create two object in one Ai or PS files and use editing of that file in these programs.
Also you can create one file with more then one artboard in Ps or Ai. Each of decals must be placed on seperate artboard.