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.

I am trying to learn more about .ytm file, so my goal is to remove all the unused variations for JotaPXModz's Juliet Starling. (here: https://www.gta5-mods.com/player/juliet-starling-from-lollipop-chainsaw-ped)

It's fairly easy to remove all the other variations but I'm having trouble with hair.

The hair got texture like this in the original file:

    <Item>
      <hash_AECFE243 value="27" />
      <hash_A7431FBA value="0" />
      <hash_4A92222A>
        <Item>
          <texId value="1" />
          <hash_36896D17 value="255" />
        </Item>
        <Item>
          <texId value="2" />
          <hash_36896D17 value="255" />
        </Item>
      </hash_4A92222A>
      <hash_92E68DB3>
        <hash_A893A361 value="false" />
      </hash_92E68DB3>
    </Item>

It appears to have two texture variations. HOWEVER, it only work as this. If I remove the first texture, then the texture is mismatched. If I remove the second texture, then it becomes transparent.

Could anyone explain how this work? Thanks a lot!