Perth - Singapore flight is 5 hours
Perth - Shanghai flight is 8.5 hours
...and I think if I am not mistaken, Singapore - Shanghai flight is about 3-4 hours?
Now why would you want to do that? it is very comfortable as it is.
If you must reshell it, I don't think it's going to be a problem, as there are a number of triple hybrid CIEM out there, even five-drivers hybrid CIEM (UM Merlin and Rooth LSX5)
Actually, a lot of Head-Fiers have had trouble reshelling dynamics in the past due to the fact that the rear needs air flow. Not saying it can't be done, but it generally hasn't been done.