Replace the original EPK file in your Eaglercraft directory with your new one and reload the game. If textures are pink/black, the path is wrong. If sounds are missing, check the filename format.
: Browsers sometimes clear local storage, so it's vital to "back up" your work: In the Singleplayer menu, select your world. Export EPK File . This downloads the file to your computer for safekeeping. Moving Between Vanilla and Eaglercraft Eaglercraft 1.5.2 Epk Files