It seems it doesn't work for me.
If I just unpack and repack, it works ok.
If I modify the 6315_1.zip with a different "apns-conf.xml" (only file I tried) it will report corrupt FW on any cold or warm boot and erase all my apps/configs until I restore the unmodified 6315_1.zip
@surfer63 : I tried one of those Joying Firmwares, it worked ok, but gave me the yellow bar. Edited the fyt.prop to be FYT=1 and saved it (it had a good amount of symbols in it) and the reflash wouldn't boot. Are manufacurers doing weird things to the FW now?