You cannot. As simple as that. The skilleffects (ANI01, BOW, DEFAULT, etc.) are hardcoded. It is listed inside the source code which race should pick which animation on which skill declaration at which skill animation.
E.g. if you decompile Terraria (the simplest way learning C#, imo), you will figure out, that every asset like every skill effect, "animation" (which are simple grid switches on a single texture file) are hardcoded. By adding a new texture file, or whatever you are up to, into the assets folder, you won't see anything ingame, unless you declare and define it directly at the source code.
Silkroad is semi programmable. You can just re-define already existent stuff at the text files (skilldata_, skilleffects, envsndeffects, etc) but you cannot declare new stuff (classes written or expanded inside the source code).
Weapon and armor models are something way more different, btw.
No one will be able adding new animations without the src.