He's not (barring reversal on appeal) immune, or this case would never have reached a judgement.

> On the other hand, if the judge wanted to see this change, requiring Twitter to both remove (his) block button and unblock all existing users (from his account only) would more likely happen.

Judges don't have unlimited freedom to arbitrarily issue orders directing labor of nonparties to a case just because they suspect s party might not respect the judgement. There are, in any case, processes for addressing failure of a party to respect a judgement, which Trump is no more immune to regarding this judgement than he is to the case resulting in the judgement.