minecraft-datapacks/resourcepack/assets/minecraft/models/block/piston_head_sticky.json

{
    "parent": "block/template_piston_head_sticky",
    "textures": {
        "unsticky": "block/piston_top_sticky",
        "side": "block/piston_side_sticky",
        "unsticky_side": "block/piston_side",
        "platform": "block/piston_top_sticky"
    }
}