creating a snapshot (and inserting it as a snapshot) is not recommended. Snapshots are a temporary replacements for other events, basically meaning they aren’t really part of the past. However, it is possible to create some sort of “SomethingImportedEvent” that contains data relevant for the first state of the aggregate. It’s not really a snapshot, just a big event describing initial state.
In some cases, it is possible to deduce some of the past of an aggregate from its current state. In that case, you could re-use existing events to build that state in the event store.