Seems like you want a custom cartridge They exist, e.g. https://www.coolspotgaming.co.uk/products/custom-game-boy-advance-game https://www.coolspotgaming.co.uk

Seems like you want a custom cartridge They exist, e.g. https://www.coolspotgaming.co.uk/products/custom-game-boy-advance-game https://www.coolspotgaming.co.uk/products/custom-game-boy-ad... ( I haven't used this service ) This seems like a good mid point between a $500 cartridge and having no friction between games