Mine passed after the changes. Engine has 150k+ (taxi) miles on it and the smoke density reading was 0.08 1/m out of the 1.5 1/m limit. There was also no advisory or mention of any visible smoke from the tail pipe.
I did make sure to run A double shot of millers additive and nearly ran the tank dry before refilling with BP ultimate diesel a couple of weeks before having the mot, weather it made a difference I can't say but in my mind it couldn't make anything worse.
Ultimately it's down to the tester. Keep in mind I am limited to only 2 places in my town that's allowed to issue mots for taxi vehicles and there are no special exceptions for taxi drivers or shady "I'll put it through this time" business going on.
With all that said, my next car will still be a petrol, I never want this hassle again.