Ok today I will try to do my best clear Feature Request!
Today I suggest you to Edit Home Screen Background and Loading Terrain Background
Also as you must know, it is possible to do it without mod elements or things Manually in files I will show you how to do!
1) First things Loading Terrain
As you see I replaced the Dirt Background with Fire Stone of my mod [Mod name is Elemental Masters]
How to do?
Step 1: You need to go to C:\Pylo\MCreator182\forge\src\main\resources\assets\minecraft\textures\gui
Step 2: You need to remove/edit/replace the options_background by another Images/texture of (The Image is normally dirt)
Step 3: After Replacing the Images REMEMBER to keep the image name "options_background" or it will not work
Last Step: Open MCreator and go to testenvironment World to see if it work :D
2) Minecraft Home Screen
From this panorama!
How to do?
Step 1 : Go to C:\Pylo\MCreator182\forge\src\main\resources\assets\minecraft\textures\gui\title\background
Step 2: You will see 6 Screenshot of images with their name and a kind of Bar
Step 3: The Screenshots are capturing the 6 side of the players, you need to do same for your Minecraft Home Page
Step 4: Go somewhere in your world you would like to be Home Page and take a screenshot of all side
The sides are North , East, South, West, Up, Down
The Screenshot SHOULD be named and arranged like this!
North = panorama_0
East = panorama_1
South = panorama_2
West = panorama_3
Up = panorama_4
Down = panorama_5
Step 5: Replace the old panorama_X by your new ones
Step 6: Open MCreator and test it in testenvironment world :D!
Here is an example of How I made mine!
BIG HELP: If GUI is not here in your folder C:\Pylo\MCreator182\forge\src\main\resources\assets\minecraft\textures\GUI
You can create it yourself by creating a folder "GUI"
Inside you put "options_background"
You put a folder called "Container" and one "title"
Inside title you put another folder called "background"