The copper horn crafting recipe, unlike other crafting recipes provided, is not data-driven. This means you cannot change the copper horn crafting recipe with behavior packs at all.

You can check the if there is any recipe folder inside these folder:
C:\Program Files\WindowsApps\Microsoft.MinecraftUWP_1.18.3026.0_x64__8wekyb3d8bbwe\data\behavior_packs\experimental_vanilla_experiments