Although he should have never dropped Herrera on the bench in the first place, I'd give him a lot of props in giving him the chance/faith to start this important game and also the foresight to let him continue into the 2nd half.
I also think bringing on Hernandez and Young was a good move. The obvious choice would have been to bring on Fellani but in terms of seniority, those two deserved their chance more (due to their match fitness, not having got sent off etc). It sets the tone for everyone get's a fair whip. I still think it's a slightly dangerous 'perform because I gave you a chance' mentality because whilst that might instill fight and responsibility in some, it also brings fear of failure and lack of comfort. Take your pick really.
It'd be interesting to see what he does with Januzaj now. Will he be relegated to the bench for 10-15 cameos or will he still get starts?