All right, no one replied before I find out myself...
After play around the value number, here are the findings:
File structure and parts info: https://forums.gta5-mods.com/topic/5458/editing-ymt-files-for-ped-variations/14
hash_C8F5438B value appears indicates the number of total textures for that part.
I still don't know what hash_AECFE243 is for, but together with "texId value" they control the texture naming, there are whi, bla, uni etc, AND 0_a, 0_b, 0_c, 1_a etc... I solved my problem by changing texture name.