For the “spaghetti legs” issue (deformation of the legs when creating a customised ymt) I found that adding the model name into the ymt itself resolves that. Unfortunately, the reins remain non-existent and I am sure Arkaus is right about having to add the model to reinsdefinitions.xml and ymt and then streaming that, but we still can’t stream because HORSE_REINS_FILE remains unsupported.
I’ve found that we can also name the model whatever we want to, for instance, I named mine a_c_horse_friesian_blackstar and it spawns just fine.
Hopefully sometime soon we can see HORSE_REINS_FILE being supported. One can dream.
Here’s a_c_horse_friesian_blackstar it is a RedM port of the smokey black star friesian but a bit larger (bigger than the mod file, smaller than the raven black Shire)
EDITED TO ADD
I did not mention this here but I think I may have in my stream.
You can replace the game horses using this method and the reins will be fine. It’s the adding of additional custom coats that does not work.