Your first option is to go in the configuration screen from the mods list menu, and put "Render selected arrow on bow" to false. The bow will look just like vanilla until the bow is actively used. (Note: may need a resource pack refresh). Select the "bow" option under "Custom Item Renderers" to also remove the arrow layering on bow use. (Note: may need a game restart)
For further customization, the modded bow models are located at: assets/battlegear2/models/item/bow_'arrow'.json You can edit those in the mod file or through a resource pack. Either way is fine.