Usually to change the CSC you have to flash the new firmware (which you have done) but then also flash to change the CSC. - On previous Samsung's (Note 3) - you have to flash the firmware, wipe the device then insert your SIM and it changes to your region.
This *may* apply to the S5 also, but only way to actually tell would be to do it, extract the CSC info and flash it. If you're unsure how to do this, then I'd hold off for a little while until others have tested different methods or release a guide on how to change it.
// LG G3 (D855) // Stock // Stock //
S3(White) > M7(Red) > Note 3(Black) > Nexus 5(Black) > M8(Gunmetal) > LG G3 (Titan Grey)