To achieve the success we witness today, Oda has time and again tweaked the elements in One Piece, steering the narrative in different directions.
One Piece stands tall among the most celebrated anime/manga franchises today. While the story's success results from various factors, we can't deny that Oda is the 'mastermind' behind it all.
With over two decades in existence, One Piece has brought forth numerous tales, unique characters, and much more. However, several aspects have undergone changes at various points to better align and here are 5 standout details.
Oars' Towering Stature

Oars, the colossal undead ranked 900, stands as a distinctive corpse in Gekko Moriah's Zombie Army from the Thriller Bark arc. Moriah implanted him with a stolen shadow from Monkey D. Luffy during that arc. Known as a member of the ancient Giant race, Oars boasts a size three times that of the largest giants, exhibiting unusual traits for giants. With this extraordinary height, Oars earned the moniker 'Continent Puller.'
However, few are aware that Oars' height underwent changes. Initially, the ancient giant's height was said to be three times that of an average giant, reaching around 12 - 13 meters. This implies Oars' height was approximately 39 meters. Nevertheless, this information was altered in a Vivre Card.
The height of an average giant was initially recorded as about 20 meters, with Oars standing at 67 meters. Not only Oars, but Little Oars Jr.'s height also underwent modifications. Initially towering at 37 meters, the Vivre Card information was changed to 60 meters.
Whitebeard's Pirate Flag Emblem

Whitebeard, a legendary pirate, was known as the 'strongest man in the world' and a former Yonko. His pirate crew bears a unique emblem on their flag, featuring images of bones forming a cross (+) with a skull in the middle, notably with a mustache resembling their captain's.
Before Oda made this image the symbol of the Whitebeard crew, the author once depicted a swastika (卍) in the skull's center. In Japan, the swastika symbol is closely associated with temples and good fortune. To avoid future complications, Oda later replaced this symbol with the bone motif.
Mochi Mochi no Mi Devil Fruit

The Devil Fruit Mochi Mochi no Mi is currently wielded by Charlotte Katakuri, the second son of Big Mom. With this Devil Fruit, Katakuri can transform his body into mochi at will, possessing a capability that instills fear in many.
Initially, author Oda introduced this Devil Fruit as a Logia type. However, this sparked fan backlash as Logia types have always been closely tied to natural elements, while mochi is not part of these elements. Ultimately, the author rectified this by stating that the Mochi Mochi no Mi is a unique Paramecia.
Character Design of Chopper

Tony Tony Chopper serves as the Straw Hat crew's doctor. Hailing from Drum Island, he is the only crew member born in the Grand Line, the fifth to join, and the youngest member on the ship. Chopper is often underestimated in combat ability but beloved for his cute design. However, few know that Chopper's design has actually evolved over time.
When author Oda introduced Chopper, he initially resembled a wild animal. However, this changed after strong support for Chopper's design surfaced in the anime version. Consequently, Oda gradually altered the design to its current form.
Vivi's Role

Nefertari Vivi holds significant influence in the Alabasta arc. In this segment, Vivi initially had to battle alone against Nico Robin, Crocodile, and all the agents of Baroque Works, who were attempting to overthrow her father's rule and seize control of the Alabasta kingdom. It was only then that Luffy and the Straw Hat crew appeared to assist her.
Interestingly, Vivi was originally conceived as a regular character, with her hair tied in a ponytail. However, when Oda designed Vivi with loose flowing hair, he felt she suited the role of a princess better and thus altered her character's role.