First of all, just wanted to correct the terms used...it's not an ECU update, but a PROGMAN update via SSS...(i assumed, since you're talking about modules being updated)...Why are you updating? are you getting errors@faults? (e.g.-active steering, airbag etc....)
well, to answer your question, since your car's a jap spec, you're facing a high risk of frying your CCC...(from my experience of observing progman updates to a jap spec, confirm your CCC will go "kapuuut"...) it's not compatible with PROGMAN via SSS for EU/MYS spec...
from what i've seen through experience, the only PROGMAN update that went well was version 22.x...but, if you're planning to update via SSS to the latest version (ver 28.x), i can say that 70% chances that you'll have negative results... you might be able to update@troubleshoot all your modules error, but your CCC will definately fry...
Anyhow, it's up to you...i'm just giving you my advise..."Don't repair what's not broken"... i can bet that they're telling you that the dealer/workshop won't be responsible for any screw-ups, right?