Naaa, this can't be piracy as modding the original textures would also be piracy as you use the original content, modify and repack it. With your comparison every cosmetic mod on nexus is basically piracy as the original files were extracted, modified and repacked. As this DLC will be (as in Skyrim) non-payed content it could not be a problem to give users the possibility to chose which optimization the want in the end instead of being forced to take it or leave it...