Just a reminder that providing specifics on, sharing links to, or naming websites where ROMs can be accessed is against the rules. If your post has any of this information it will be removed.
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There's no divine scripture that says you have to include the D/N System in your game, it's an option to enable/disable at your leisure. However, if your main basis for removing it is because you don't like the look of it, might I suggest you look at Deo's Custom Day & Night Shading? It makes the Day/Night transitions look so much better, and less hard on the eyes.
A link to it can be found here: https://www.pokecommunity.com/threads/372400
I have that my problem is that I'm making custom battle backs for ever area and I really annoys me that there is no morning battle back so when it's orange outside it's still the normal background along with how annoying it is to try to get the colors for the backgrounds to look right with the shading of each time.