As charles25565 said, it will no longer be GrapheneOS.
Also, once you create your own build/fork of GrapheneOS, it won't receive updates - which means that business will have to rely on you to keep their phones secure and updated. You will continuously be developing/maintaining and porting updates from the GrapheneOS repo to your custom build, which will likely run into bugs that you will have to test, fix, and may cause undesired issues for that business. If I was that business, I wouldn't take the risk.