About snapshot recovery

Does ES plan to allow changes to the "number of shard" when using snapshot recovery in the future?

Welcome to the community :)!

Parameters allowed to change during restore are described in the docs.

But

Some settings such as index.number_of_shards cannot be changed during the restore operation.

So no, you can't change the number of primary shards during a restore. You can change the number of replica shards as per the link above. To change the number of primary shards, after restore you'll have to do one of: