i've seen this post
backup full sms/mms contents via adb
but i know that kitkat changed some stuff to do with sms so i don't know if this is still correct.
Can someone more knowledgable than i please confirm?
(the reason i want to do a manual backup of sms/mms database is summarized here http://forum.xda-developers.com/android/help/disable-touchscreen-z2-t3080520)
got impatient and tested this out myself.
This still works for kitkat.
copied both
/data/data/com.android.providers.telephony/databases/mmssms.db
/data/data/com.android.providers.telephony/databases/mmssms.db-journal
using the method outlined in the other SO question.