It has both cape and elytra infomation, does this mean CustomSkinLoader mod can display seperate texture for elytra and cape in-game?
i tried but it only display one texture with elytra texture having highest priority

The elytra texture doesn't affect the cape texture, but the cape texture affects the elytra texture, so the elytra has a higher priority than the cape - this is vanilla feature, CustomSkinLoader doesn't intervene.
Elytra was added in a snapshot of Minecraft 1.9. At that time, elytra was still a separate texture, not bound to the cape. This feature has been retained to this day.

is elytra still a seperate texture in 1.18? im using a skin server from https://github.com/yotsubar/CustomSkinLoaderAPIServer and look like changing only the elytra also make the cape texture changed

Can you provide the logs of the CustomSkinLoader when you upload the elytra separately and enter the game? It's the CustomSkinLoader.log located in the .minecraft/CustomSkinLoader directory.

sure
CustomSkinLoader.log

it's a bug of CustomSkinLoader. Thanks for reporting!

no problem, im happy to help ^^

this issue should be fixed in the latest build

Forge
1.7.10 ~ 1.16.5: https://csl.littleservice.cn/mods/CustomSkinLoader_ForgeLegacy-14.13-SNAPSHOT-314.jar
1.17+: https://csl.littleservice.cn/mods/CustomSkinLoader_ForgeActive-14.13-SNAPSHOT-314.jar

Fabric https://csl.littleservice.cn/mods/CustomSkinLoader_Fabric-14.13-SNAPSHOT-314.jar