I have found one reg tweak to disable threaded sms in KAISER forum of xda develpoers .. I tried in ELF and it works like charm..
you need to create OEM key in Settings and create a DWORD SMSInboxThreadingDisabled and set it to 1
reset the device and you are now back to normal SMSs..
It also does not disable SMS notifications..
I searched but didnt found if it is already in forum.. If it is there dont bash me