If Maggie had done similar I'm sure it would have been engraved on your mindIt is a long time ago. Almost 20 years. I had to refresh my memory about how that election transpired. And reading Wikipedia it is pretty clear Blair did nothing wrong. It wasn't a decision made by the Leader but by a combination of MPs, MEPs, union members and Labour members. Then when Livingstone lost the vote he reneged on his promise not to run. This really is a completely different situation. If you want to justify Johnson's actions with this I can only shake my head in a combination of horror, amazement and sympathy.
Blair did nothing wrong if you mean against the law - but he did rig the voting to ensure that Ken didn't get chosen as the Labour candidate. And Ken did the right thing to renege on his promise after that - and the final result showed he was right to do so.
At the next mayoral election Blair was forced to accept him as the Labour candidate.
Again it's not a case of justifying actions - its pointing out what things were and could be like again under a Labour government.