I haven’t heard of any best practices regarding migrating accounts other than just make a new account and start over. Apps that log you into lemmy/kbin/mbin etc might try and solve that by having all your old posts get mirrored to an instance on your new account but it would have to be in a way that does not spam the other instances version of the community the posts were shared to. I guess if you use a timestamp on posts you could have the migrated posts appear before the newer ones after migrating?