Can I apply for a Visa S1 in South Korea?

If you cannot provide the alien registration card in South Korea (ARC) with at least 6 months remaining validity, you cannot apply for a Chinese S1 type in there. But you can try to convert the S2 into S1 at the exit and entry administration of the local PSB within China. If it can succeed, you don’t need to go back to your home country for that. Just give it a try!