Yes, Red & Wiz, there is also such a clause (if I'm thinking of the same one as you) within our regs around the concept of "technical assessment".
If the manufacturer has carried out a detailed scientific assessment, from the actual evacuation demonstration completed during cetification, which shows that a reduced number of seats with a coinciding reduction in cabin attendants will still enable an evac in 90 seconds then some NAA's may accept this.
I understand CASA is lothe to accept this menthod as it is just a calculation and not the result of an actual demonstration. One step too far from the ultimate safety case - the demo, for CASA's liking. Must say I would sit in their camp on this one. An exemption in Oz in such a situation has been done once in recent time, but I doubt it will be accepted again, unless of course there is a change of CASA assessment personnel (which happens all to often
) and someone tries again.