Hair dye is an absolute blast and I'd love to recommend my own hair dye brand.
(Special Effects- costs 10 dollars, doesn't fade quickly, doesn't look terrible faded, no animal testing, easily ordered online, bottle can be closed and the dye doesn't dry out, can be re-used)
I went through high school wearing short pink hair, dressing punk/ska style. I was covered in safety pins and made most of my own clothes. I believe it's one of the best decisions my parent's made, to let me dress how I want , especially before having to join a workforce that may not appreciate my style. It let me explore who I am and who I want to be, let me explore other people's perceptions, and taught me a lot of valuable lessons about pre-judging. It encouraged my creative side, encouraged me to DIY and to value money and recycle (I LOVE thrift stores now and hate chain stores, feel like they have too limited options most of the time, nothing unique). The only limit they gave me was nothing permanent on my body that could be seen by people at the grocery store unless I dress immodestly (naval rings for example, were acceptable as a teenager, but my lip ring had to wait until I was at least 18, and even then I waited until I was 23 and knew I could obtain devices that would keep it from closing but would hide my piercing, like these http://compare.ebay.com/like/130495324065?ltyp=AllFixedPriceItemTypes&var=sbar&rvr_id=220592186392&crlp=1_263602_304662&UA=%3F*F%3F&GUID=fcdcaffa12c0a0e1e4e0b8e0ffc8be2b&itemid=130495324065&ff4=263602_304662
I never dressed immodestly in high school, but still enjoyed my belly button piercing, mostly because it helped me overcome my crippling fear of needles.
Plastic surgery however, I'm inclined toward not being so approving of. These other modifications, piercings, tattoos, hair dye, always encouraged a sense of being myself, enjoying and ornamenting my body, plastic surgery just seems like the opposite of that, changing because you don't like your body, not because you are enjoying it. That's how it seems to me anyway. I've considered plastic surgery for my weight issues, because I gained weight from medical problems and have had a lot of trouble losing it, so I can understand wanting to fix stuff, but I'm still inclined to encourage loving yourself as you are, adding for fun or for expressing yourself, not to hide something you aren't comfortable with.
Anyway, whatever you do, be calm and reason with your kid. You really don't want them deciding to do things to get revenge on you for perceived meanness. It would suck to have a tattoo you'd regret later that you got out of angst. Always explain why they can't, and hell, why they can do things. Some kids want this stuff so they can feel adult, and "because I said no" feels like child treatment, and can make them want to rebel with it. My appearance in high school was non-rebellious. My parents loved it, and I loved telling my friends how cool my parents were. We connected over it, and I think that's totally valuable. Even when I did stuff they thought was ugly (one parent likes my lip ring, the other doesn't), they still liked that I feel like I can be myself, be smart about my choices, and have some fun.
That's my view anyway.