You just need to put texture pictures in kuebjs/assets/kubejs/textures/item/ The texture file names should be bow_golden.png, bow_golden_pulling_0.png, bow_golden_pulling_1.png, bow_golden_pulling_2.png
You can also modify existing bows with ItemEvents.modification like this:
Minecraft modder building compat, gameplay systems, and mob behavior — designed for modpacks. Mainly develop on 1.20.1 Forge. Can support 1.21.1 Neoforge, 1.20.1 Fabric, 1.21.1 Fabric.