If China does this, it will cause the dollar value to fall, making the price of their products higher. Coupled with high energy prices and therefore high costs for container transport, it could trigger a lot of job creation here or elsewhere, and China exports to the US will take a big hit.
No, the cost of their products won’t go higher. They have the yuan pegged to the dollar. The dollar goes down, the yuan goes down.
Their biggest hit would be in the cost of dollar-denominated goods that they import, especially oil and diesel fuel.
This is why there is no such thing as “Free trade” with China. As long as they maintain the currency peg, they have the upper hand.