What do you think would happen if one could basically 'become' a fantasy character, powers and all, through implants and other body/mental modifications?

This is the basic concept of my Sci-Fi world.

"Implanted devices can now change people's top movement speed, their charm, and even give them what can only be equated to superhuman abilities like calling lightning with a single thought. Alteration Engineers are constantly working on and testing new products for the people while the Transformation Artists sell them and do the procedures, barely leaving any evidence in most cases. A person can now tell an Artist what they need and the Artist will give them ideas, much like at a tattoo parlour.
"Many people buy 'Alteration Packs'; a single procedure that gives multiple changes to oneself. Some common Packs are the Rogue pack, commonly used by criminals, but also sometimes used by spouses and lovers for various reasons, the Bard pack, as seen in salespeople and artists of all kinds, and the Elf pack, which is used by all law enforcement to be able to see through alterations like the Silver Tongue. Some people don't need Alterations to be able to see that they're being deceived, but the Elf system is a good precaution.
"There are also cosmetic Alterations. The Elf pack, for example, gives the option of adding pointed ears to signify to people not to bother trying to use any Charms on the person. The others can add horns or tails, if the person so desires. There are many examples, but the effect is the same; people know. They know that the person probably has Alterations and that they don't want to get on that person's bad side."

That's super cool. Love the idea. The only thing you would have to look out for is imperfections to the Pack. If there is any battery life, if there is a signal that could interrupt any sort of transmission or if there could be a problem with placement, say one gets ripped out or so. I might also look into where the human body is weakest. With implants, would there be any sort of pain after the implant? Could this be eradicated with an easier implant system? Also, how would you keep fakes from, say, a black market if you want it to fully develop a culture around it? I might also consider the ramifications of personality change and how to keep that from occurring.

So its Syndrome from The Incredibles? Kinda like that line "When everyone is super, no one will be." Or maybe it becomes another method of self expression. What if someones genome makes them unable to be modded?

I like the general idea. It seems it could cause another layer of chaos to enter the world, unless it was moderated somehow.

This is a pretty cool basic idea. You mentioned a little thing about law enforcment, but what about law makers? How have they limited these divices? Why were they created in the first place? The only reason something would be sold to the general public is of they asked for it (supply and demand). You know, people complain about mops and so Swiffer gets invented. Everyone buys it. Money in the bank for the creator of Swiffer. But who would want to create something as chaotic as superpower surgeries to sell? Where'd they get that idea? How were they certain they'd be able to make a profit? Would they have to wonder if there would be a world that was able to give them money on the end? Or did this maybe start as governments worldwide commissioning a huge team of scientists to create similar technology for enhancing quality of life throughout the world, but then when certain corporations got their hands on it, they turned it into a superpowers thing?

Perhaps it started as a special military project. Then the public found out and demanded to get super powers.
It could have started as a breakthrough in technology. Then one corporation runs a monopoly over it until ideas are stolen by others.
An important question to ask yourself is "Is it cheap" or just for the elites and military. Can the power be addicting. Can someone be modded to the point they lose their minds. Are their side effects like mutations, or the body not being able to withstand the power. (In the example of someone summoning lighting could they electrocute themselves.)

So could you get multiple packs? like "Oh I have the Demon Pack which includes a robotic tail you can control with your mind, and wrist mounted flamethrowers (with fireproofing to go with them, of course!). I also got the Orc Pack, which gives me enhanced smell, hearing, strength, and stamina. And I have…" You could get enough packs to make yourself a minor deity.

Also, could you get the same pack more than once? "So I have the Elf Pack, which includes enhanced hearing, super fast reflexes, and sped up healing. But I got the pack nineteen times, so I can hear a conversation half a mile away, catch a mosquito out the air without hurting it, and my body will naturally dislodge a bullet from itself in under a minute."

One more: Could you, instead of getting a whole pack, just get parts? "I got underwater breathing from the Mermaid Pack, but I didn't get the tail. But I did get the wings from Fairy Pack, without the plant growing or slow aging."

sorry for the long post, I don't have a potato to give you!

I scared everyone away with my looong post

This is actually really interesting! It's like Deus Ex Machina meets Dungeons & Dragons! I can imagine certain Packs being used more often with certain governments, like a theocracy would have a lot of higher-ups would have a Paladin Pack or a Cleric Pack. Would certain gods have an effect on what the Paladin and Cleric Packs have?