why not,its purely not an advantage mod,just a cosmetic,it doesnt change the gameplay or give you an advantage

dont forget about that cape mods are allowed mostly in servers

it would be more work to the verifiers to check every mod you are using, that's why mods are whitelisted. you can get custom capes without mods by following this tutorial:

So is cape mods allowed?if not make it allowed

cape mods are not allowed for the reason i told you in my previous reply, and you don't have to use mods with the workaround from the video ive linked (allowed method). Using mods for custom capes is not allowed