Nope Lemmy’s blocking system is cosmetic only. It’s very much useless against defending from real malicious users. I assume the purpose it was built for was under the assumption that it was going to be used exclusively by easily offended snowflakes, which is backed up by the way that most users treat a person’s claims regarding a malicious user or malicious instance.
Just to be clear if you do engage in trolling or bad behavior they may block your insurances as well. Not necessarily saying that you will but I know that some have tried. Yes there are tools that let you bypass the federation or you can just get new domains but that’s called circumvention and could be considered a cyber attack.
Great, if ActivityPub isn’t working out for you and you can’t stand defederation then there’s the door.