Is it possible that the books of Hadith could be distorted, even by one percent?

If the intent is to claim that the books of Hadith (definition) were distorted, or that they are fabricated, or that something not belonging to them was introduced into them, then this is false and a slander. The Ummah has unanimously agreed upon the authenticity of their attribution to their authors. As the scholar Ibn al-Wazīr al-Yamānī explained, the books of Hadith received extraordinary attention in terms of audition (samāʿ), meticulous recording, and verification, and their attribution to their authors is known by necessity. The fabricators despaired of adding anything to them. Furthermore, the variation among their different recensions increases the certainty of their authenticity. However, if the intent of "distortion" is the presence of weak and fabricated narrations within them, then this does exist, but scholars have exposed its falsehood and warned people against it, as Ibn al-Mubārak said: "The discerning masters live for it [i.e., for distinguishing it]."