From what I have understood there is no way to pause the syncing, so my understanding is that you would have to use a different realm file and then copy the data over.
With MongoDb Realm it seems like it is a lot easier to keep the data models the same in the local realm and a synced realm, but I don’t think this is an easy use case.
I plan to do something similiar though. In my app, each user can do well over 1000 edits during a session. If I would commit each of those write transactions to a synced realm it would be expensive. What I was recommended to do in this case was to do my edits locally (on a local realm) and then copy them over to the synced realm when done, which would drastically reduce the sync operations used.
Not sure if this helps, but I’d also think thought the database structure from the start to make it easy to move between realms. In my case, it means avoiding relations and top level objects when necessary and favor embedding documents. If one document is a separate unit with few dependencies it would be easier to move the data from local to synced and back.
Not sure if this helps, but this is my 2 cents.