I did this on my instance. You create a new user and give the script those credentials, it goes out and subs to all the trending communities across the various instances so now my instance has a big mish-mash of communities federated, not just the ones I originally subscribed to on my personal user.
I can’t seem to find it in a Google search now so I’ll take a look at my server in case I ran the script there and saved a copy. There appear to be a lot of similar tools now to assist with people moving over from Reddit but this script was really quick and handy.