How to migrate only a subset of data from another server

Looking at the CLI docs I am missing options to control export import. further
I can export everything into json and import everything elsewhere.

This is not how we want to do migration.

We would like to select channels and also drop previous users.
How can this be done?
What happens when I select a subset with JQ from the json export and try to import it elsewhere?

This goes into the question how fault tolerant the import is in replacing missing references with something that doesnt break the system.

Any ideas on this?

Welcome to the Mattermost Forums @uvwild!
I’m wondering, do you have the ability to access the SQL Database?
I know it is possible to dump to an export file the contents of a table (such as the Mattermost’s database table that contains the chat message posts) based on a parameter (in this case, the channel ID) being present, and ignore others.

I belive that this would give you the ability to export, and then import the conversations back into a new Mattermost instance’s database, if I am understanding your question correctly.