Developer Marc Robledo has just released two tools for fans of the Super Game Boy: One that allows you to create a custom border when the SGB is loaded and another that allows you to inject a custom border into individual Game Boy roms. I’m pretty sure the SGB border can only be used with emulation, however the game border injector should work on original hardware using ROM Carts, or manually flashing a ROM to an individual cartridge. More info after the links:
Border Converter: https://www.marcrobledo.com/super-game-boy-border-converter/
Border Injector: https://www.marcrobledo.com/super-game-boy-border-injector/
Super Game Boy Info: https://www.retrorgb.com/supergameboy.html