This holds, and will keep your pool and your shares in the process.
As you could host two full pools, an alternative would be to simply create “newpool” (8*18TB) and replicate from “oldpool” to “newpool”. Benefit: You keep “oldpool” as backup, and could use it as a pre-filled replication target. Drawback: “newpool” has a new name, so you have to either readjust all your shares to the new name or rename “newpool” to “oldpool”.