Thomas Weber's book Hitler's First War is probably the definitive study of Hitler's First World War service. Weber concludes that Hitler did deliberately obfuscate his war experiences to create a suitably heroic tale to support his political career, however it does not appear that the Nazis deliberately altered archival records.

Hitler, far from the heroic dispatch runner who saw the war as his political education, was in fact in the Imperial German Army's parlance, a "rear-area pig". Much of his war was spent in the relative comfort and safety of the headquarters of the 16th Reserve Infantry Regiment, and Hitler deliberately conflated his job - running messages from regimental HQ to the battalion headquarters closer to the front line - with the exceedingly more dangerous job of the battalion and company dispatch runners, who had to run messages directly to units in contact with the enemy. Hitler actually refused to seek promotion out of fear that he would be transferred out of his relatively safe billet. This is not to say that Hitler was never in danger - he was wounded in the Battle of the Somme, after all - but the fact remains that his experience of the war was incredibly different to the men on the front lines and was one of considerably less stress and peril. It was therefore something that Hitler could easily romanticise in his post-war writings, but also something that he needed to inflate and obfuscate.

Even the circumstances behind the award of Hitler's two Iron Crosses are murky. His Iron Cross, 2nd Class, awarded on 2 December 1914, was apparently awarded for his role in pulling the regiment's commanding officer, Lieutenant Colonel Philipp Engelhardt, back into cover after he exposed himself during the First Battle of Ypres. However, according to a citation written in 1915, as part of a brochure commemorating the regiment's war service thus far, Hitler was part of four dispatch runners who were worried that Engelhardt had exposed himself and warned him to come back, rather than a more valiant tale of pulling the commanding officer back through enemy fire. According to that same brochure, the real hero of the day was Hitler's comrade Anton Bachmann, who actually did carry a wounded man through French fire to safety. Bachmann was later transferred out of the regiment and was killed fighting in Romania. The award of his Iron Cross, First Class in 1918 is even more mysterious, and Nazi propaganda delighted in telling tales that Hitler had singlehandedly captured several British (or were they French?) soldiers. What does seem certain is that Hitler owed his medals not to any special bravery on his part, but rather to his close contact and good relationship with the officers of the regimental headquarters.

Hitler was also blessed with extraordinary luck: he missed a particularly devastating period of combat at Bapaume in 1917 because he had been sent back to Germany on a course. While I would agree that being injured his not especially lucky, the injury he suffered on the Somme on 5 October 1916, after a British artillery barrage struck the regimental headquarters, took him out of the battle after only four days of fighting. He therefore missed the grinding attritional combat of the Somme, and both experiences meant that he was unable to understand why morale and fighting spirit were dropping so precipitously in the German Army be 1917. Hitler also made sure to glamourize the circumstances of his injury in Mein Kampf, implying that he'd been on the front line at the time and that he'd had to hobble back to the rear.

In summary, Hitler did obfuscate his military career for political purposes: his post was atypical for German soldiers during the First World War, and he and others like him were largely despised by troops on the front line. Fortunately, much of the Bavarian War Archive was still intact when Weber did his research for Hitler's First War: it does not appear that the Nazis deliberately altered the records of the 16th Reserve Infantry Regiment. They were, however, extremely selective in the stories and testimonies of Hitler's former comrades that the chose to publicise, creating an image of Hitler as a heroic soldier that to some extent, is still believed to this day.

It depends what you mean by 'records'. To my knowledge there is no suggestion that fake citations were created and inserted into the military archives, but certainly, how Hitler's achievements in WWI were portrayed to the public were inflated and didn't reflect the factual record. This older answer might be of interest for you.