the question is: did YOU achieve something, or did your modification achieve something?
There is no "I" separate from myself - if I modified myself, then it is still I myself that made the achievement.
ObCarAnalogy: If I tune up the engine of my car and it performs better, it is still my car performing better, even though it was modified. If I replace the axles on my Jeep with stronger versions, reinforce the frame, add protective plates over vulnerable components, and I find that the Jeep can now travel into areas it could never reach before, it is still my Jeep achieving these goals, despite having been changed.
ObLoCAnalogy: If I add a book to the Library of Congress, increasing the amount of knowledge stored in the LoC, the LoC is still the LoC, even though it has been altered, and hopefully increased some small amount, by the addition of the book.
ObMeatSackAnalogy: If I put in long hours of training, my body is altered. I may eventually accomplish tasks with ease that formerly were impossible - perhaps I can run longer distances, or climb more difficult mountains. But I do not become depressed or full of self-loathing because my goals were only accomplished by self-modification - my goals were made possible because of self-modification.
ObTreeAnalogy: If a tree falls in the forest, then it is still part of the forest, even though the forest has been altered.
ObDrinkAnalogy: If I've chugged a beer after each analogy above, then I've still flargled the orglepath, even though babiggle the snookerfarthing. (And obviously if you're drinking gin instead of beer, you'd instead be snargflaffling the orglepath instead of flargling it, but the principle remains the same.)