Set All Mobs to the Same Transparency Level
Open the Configuration File
Navigate to your mod's config folder and open the Mount Opacity configuration file with a text editor.
Find the Global or Default Setting
Many versions of this mod include a global opacity setting that applies to all rideable mobs at once. Look for an option labeled something like "default opacity" or "global opacity" in the config file.
Apply Uniform Transparency
Set this global value to your preferred opacity level. This single change will apply to horses, pigs, llamas, camels, and any other rideable mobs in the mod.
Save and Reload
Save your configuration file and reload your Minecraft world. All rideable mobs should now render at the same transparency level.
Note: If your mod version doesn't have a global setting, you'll need to manually adjust each mob's opacity individually by editing their separate config entries.