I’ve used lemmy_migrate in the past and it’s good for one-way copy. I’ve also seen lasim, but I haven’t tried it. You may find other options on awesome-lemmy.
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Thanks for the suggestions. These tools seem to handle a somewhat different albeit quite similar use case, though, namely gathering all subscriptions across a number of instances to just a single main instance. I need more manual control, since I want to spread out my community subscriptions across a number of different instances, without any one of them necessarily being considered "main".
LASIM works great. Used it to migrate my main account to an alt for when my main instance inevitably goes down.
Can it be used to manually distribute community subscriptions across instances, or is it just a tool for gathering all subscriptions to a single main instance?
Downloads one instance's communities (and some other settings) to a JSON, then you can upload from that JSON to a new instance. I'm not sure there's anything that quite caters to what you're looking for yet.