Too low interest rates are pure cancer. You get zombie companies in your economy which get progressively less and less efficient.To weaken the Yuan, you will have to print money, which increases domestic inflation, or you have to drop interest rates, which although might be stimulating the economy, comes badly at a time when China is trying to make the economy learn how to tighten its belt, consolidate and correct the excesses of its earlier boom years.
Neither low nor high interest rates are a good thing.
China will have to print more Yuan to replace the trades it used to do in foreign currency with Russia. I think it would be also smart if they snapped up the exits Western companies will make in Russian businesses like in the energy sector. This would allow them to dump the dollars and euros they have for things with actual value. So they will lose less once the West defaults on its debt to China like they just did with Russia. For reference the US-China yearly trade deficit is about as large as the entire Russian Central Bank reserves they froze from Russia.