This mod allows you to add your own splashes to the title screen using a simple in game GUI
Click on the "Splashes" button in the top right of the title screen and it will bring you to the splashes GUI. From here you can type a splash you want into the box and click "Add". If you want to delete or edit a splash you can scroll through the list to find a splash, then click on it to edit it. With the splash selected you also have the option to delete the splash.
Go to the config file at config/custom_splash_text.json and set show_title_screen_button to false. This is perfect if you want to include the mod in a modpack to add custom splashes to the title screen, however don't want the user to be able to modify them.
Please let me know in the comments below so I can fix it.