Originally Posted by
KARFA
That is correct - staying on the transit at T5C or being escorted out from T5A (there is an hourly escorted route from T5A) are the only ways to swap from departing to arriving streams.
There used to be a HAL staff check at T5C but this was stopped a few years ago. However, there are plenty of signs to already tell you not to get the transit and go to B or C if your flight doesn't depart there, and at T5C the automated announcement basically says end of the transit everyone off.
Sure, but the problem is that people don't always obey the signs (cf. the blogger referred to in the original post). The real issue is then indeed at T5C and they really should reinstate the staff check there.