Is there a way to test how the game opens / loads?

I know you can test the game but is that how they game will look when a player downloads the game and opens it? Or is it different?
Also, is there anyway to change the loading screen if that is the default for the game?

I’m not sure what you mean for the first part exactly, but…
To change the background of the loading screen and the color of the loading bar (?),
Press this button on the top left corner of your screen
Might be different on your device. Then, press this button.

And in that menu select “branding and loading screen”. From there,

just replace your image, or make one with Piskel. Or change the color of the loading screen.
To change the color of the loading bar (???), scroll down.