Good idea, I just looked however and they've changed the instances page to: https://fedidb.org/software/kbin. So any server that has federated with any other listed is on there, I believe. More Kbin instances out there than I thought!
Sorry, I should have included that info. You got me thinking, however, and I made the decision to defederate from lemmynsfw.com. I'm not against the communities it hosts, but I don't want to deal with any of the content hosting legal questions that come with it (or at least minimize it where I can). There do appear to be some posts that make it in to the 'random' microblog section that are NSFW, I will look into what I can do for those.
It's not, unfortunately. The main issue I see with implementing that is all of your existing posts/comments would still link to your old account on other instances. So either your old instance would have to forward requests for your account to the new instance, or maybe ActivityPub has some way to push that update out and update your account's home across the fediverse. I don't know enough about it unfortunately.
You are welcome to create multiple accounts in any case. Suppose that defeats the purpose of the fediverse though.