Add "defmbth, dark blue hair, short hair, blue eyes, hair between eyes, black cape, black armor, black coat, black pants, gauntlets, black gloves" for his regular look.

Replace "dark blue hair, blue eyes" with "green hair, green eyes" for his timeskip appearance.

Add "enlmbth, green hair, short hair, green eyes, hair between eyes, gold tiara, gold trim, high collar, white cloak, black shirt, armored legwear, black boots" for Enlightened One Byleth/Legendary Byleth (Male).

Add "wntmbth, dark blue hair, short hair, blue eyes, hair between eyes, green cape, fur trim, santa hat, holly hair ornament, santa costume, red pants, red gloves" for Winter Byleth (Male).

Add "hwnmbth, dark blue hair, short hair, blue eyes, hair between eyes, demon horns, black suit, formal, striped suit jacket, pink ascot, belt, black pants, demon wings" for Halloween Byleth.

https://civitai.com/models/1680167/byleth-eisner-male-fire-emblem-three-houses-sdxl-lora-or-4-outfits-illustrious