Need more information. Are you stock but rooted now? Is it Lollipop, but you are trying to go back to KitKat? But you say you want a modified ROM? I'm a little unsure what exactly you are trying to do.
You certainly cab go back to kitkat by using Odin to reflash a factory image and then re-root it. You may be able to just flash a KitKat ROM-- I know a lollipop ROM won't work with the KitKat bootloader, but I'm not sure that a KitKat ROM would care about a lollipop boot loader. You need to research that if you don't want to re-flash the factory image.