I see this may need a different approach. Instead of rewriting your entire post process material or editing your current materials drastically since you have the look you want, it may be a better ideal just to exclude the undesired materials from the post processing using stencils like so:
Here is a great non-Epic affiliated example of how to apply a stencil so that your post processing volume only works on what you want it to:
This may work with your original sphere you created. I hope the above helps get you closer to the solution you are looking for!