Is a second import possible?

[shlomizadok]

I am planning a migration of a large org from Slack to Matrix and I plan to use your tool for that 🙇🏾.
It seems to me that there would be at least a small window of time between when we’ve exported data from Slack and while we’re still performing the migration into Matrix. During that time, there would be two potential events happening that I am curious how to handle:

Existing Slack users will want to continue being able to communicate. What will happen to their messages after the migration? Can I download a new dataset and import as well?
(I consider this scenario very likely, almost guaranteed assuming the migration takes anything longer than a couple seconds, which doesn’t seem likely given the amount of data.)

New users may want to sign up. If they signed up after the export, could I import them as well?

Top of head I was thinking maybe to use a federated setup for the second import, is that the right direction? Would love your direction.

Another idea is to perform a new import of the freshest data to a separate homeserver (on a different domain) and once finished to change the domain so the two servers would "know" each other and sync. Is that something that would work?

[awesome-michael]

Unfortunately I think the script would import every message again in the second import. But I think it shouldn't be too hard to adapt the script to remember the timestamp of the previous import and ignore any events prior to that timestamp in the second import.
Users and rooms are already saved in lookup tables (LUTs) so that users and rooms are not created twice in the second run.