I think it's pretty obvious that right implies morally acceptability. You can't claim to have a right to something evil. (The reverse is not true. It is morally acceptable to own a Tesla, but you don't have the right to one.) Alterations can be harmful and any harm that is not a justifiable side effect is by definition immoral. That it's your body does not somehow negate the immorality of self-harm. Indeed, direct self-harm is even worse morally than harm of others because it is in direct opposition to one's own good (arguably, harm of others is also a form of self-harm, specifically harm of one's character and will and habitus, of one's intellect because of the harm of one's reasoning faculties it entails, and harm of the common good). So you cannot say you have the right to self-harm. This is just a strange consequence of the incoherent ideology of absolute autonomy.
Now, if you have, say, a defect in your body that is preventing the proper functioning of your body, then we may correct this defect through intervention. This is restorative, that is, it seeks to restore the function due to the body by virtue of how it ought to function. This is the basis of medicine.
Another false view that can nudge people toward the view that any modification is acceptable is metaphysical materialism, also incoherent. In that case, crude metaphors between artifacts and living things are elevated to the status of the truth and since it doesn't matter what we do to an artifact per se. We can modify a computer any way we wish because there is no fact of the matter about what a computer is or how it should be apart from human intent. It is just a collection of things arranged in a particular way incidentally that puts them in a series of incidental causal relations, but there is no inherent tendency for these things to exist in these relations and no accounting for one in terms of the others except through the lens of human intent. Living things aren't like that.