Sounds like a neat idea! Here are some things I might try:
- Earrings that give you better hearing.
- Earrings that change the appearance of your ears so that a human can disguise themselves as an elf or a gnome could look like a halfing.
- Earrings that help you discern lies from the truth.
- Earrings that let you store all your money in an invisible extradimensional space behind your ears so you can pull coins from there like a magician!
- Nose rings that give you the scent ability so you can track like a bloodhound.
- Nose rings that let you detect poison.
- Lip/tongue rings that allow you to breathe underwater or speak another language or become particularly alluring or persuasive.
- Eyebrow piercings that give you lowlight vision or allow you to read really quickly.
- Piercings/Jewelry made with gems of powers you can remove and toss as one use magical weapons. Toss a ruby and it becomes a fireball, that kind of thing.
- Illusion Tattoos: A tattoo of an animal or person that lets you assume their likeness once per day.
- Weapon Tattoos: Get a weapon tattooed on you so you’re always armed. As a quick action, you summon the weapon instantly to your hand. When you’re done it returns to your skin.
- Wing tattoos that give them the ability to fly once per day.
- Skill tattoos that give them a small bonus to the skill of their choice.
- Friendhsip tattoos: Identical tattoos that let two people transpose their positions or make short range teleports to each other.
- Level 0 Spells as Tattoos: Imagine getting a cute little lightning bolt tattoo that lets you cast Spark at will, or a thread and needle tattoo that let’s you cast Mending. You could theoretically make a tattoo for any spell, though I’d make it expensive to do so for the higher level ones. I don’t know what system you’re running, but if they have rules for the Permanency spell, you can reference that to give you a good idea for costs.
Those are my ideas! To keep it balanced you should limit how many enchantments a character can have active at any given time. I hope your players enjoy their magical body mods!