Actually a large fab will have multiples ( 5-7 or more) of the same piece/model of equipment so when you move to a smaller shrink you will sequentially replace all that shrink series/size. The new equipment will be used to make the existing shrink size until all the necessary new equipment is in place to produce the smaller size. The product coming out using the new equipment on the old shrink size will be at tighter tolerances, thus higher yields and better performance which is why Intel can now offer higher performance 10900ks series CPUs on 14nm before switching to 10nm or lower.
ChiComs are large purchasers so they will buy the same series/model equipment from more than one fab around the world thus they will have spares for parts. If it was possible to re-engineer or calibrate the old equipment for the next shrink it would not have been sold.
As we all know performance improvements with smaller shrinks are incremental, so if the ChiComs purchase used equipment suitable for say 14nm, they can produce product still technologically competitive with 10nm or less but at a much more competitive price for sale/use in China, in the third world or inclusion in finished products.