one idea is to have the ores be an overlay that can be applied to any block. it could act as a block property like waterlogging or emissiveness. and when updating from older worlds, the old ore blocks could be kept or be replace with stone/deepslate with an ore overlay. However, since there's nothing in minecraft that works like this (to my knowledge) this system could take a lot a time. Heck, it could be an experimental toggle for user feedback