Disclaimer: I do not own Harry Potter or any of its characters.
'Yes it worked' Harry thought happily as he got up off the ground where he landed then he noticed something strange. He was a few feet shorter than usual so he conjured a mirror and then jumped almost dropping the mirror to the ground. He was back to looking like his eleven year old self then he did a quick spell to see the date august 13th 1940 came out in green spidery writing.
'Ah' Harry thought went back a little too far he had only wanted to go back to when his parents were in school, but then Harry thought for a moment 1940 was the year that tom riddle AKA Lord Voldemort started school.
'Hmm' Harry mused 'this could work to my advantage' 'I could help tom through school and make sure that I get my revenge on the potters the order and Albus Dumbledore himself.'
So with that thought he changed his appearance to look more like a child model than anything to make sure that when he goes to school he's noticed, since Dumbledore would have a harder time manipulating a student who is constantly the center of attention. However Harry kept his voice the same since soon after he left Hogwarts he learned that people loved listening to him no mater what he was talking about, and he was extremely persuasive. And yes when Harry set out to master all the types of magic he left out nothing so he was a master in the beauty spells and even learned some that couldn't be reversed unless you used a password so he set the password to his new look to be I Am Harry James Potter in Parseltounge.
Once satisfied that no spell could penetrate or detect his new looks. Harry took his multidimensional trunk out of his pocket enlarged it then opened the third compartment where his house was located, then put up a bunch of advanced wards to repel muggles and wizards from the area. Then he descended the stairs. As Harry sat down on his favorite armchair he thought about how he would act during his Hogwarts years, but then he realized if he wasn't brilliant tom would want nothing to do with him and he would be less noticeable which he couldn't let happen. He had to always be in the spotlight and if he spent a lot of time in the library it would explain his knowledge of things that surpass his first year curriculum.
He would also need a new wand incase someone cast the prior Incantato which would show all the spells cast by that wand to whom ever cast, it and there was a war going on back home he had cast his fair share of unforgivable's. But then Harry remembered that the prior Incantato wasn't invented for another twenty years with that knowledge, Harry decided to make a list of all the spells not invented yet so he wouldn't accidentally use an unknown spell in front of someone by accident. He also went around his house putting everything that wouldn't be invented yet into a small bag charmed to be bigger on the inside than it was on the outside, and then he put it into a cupboard and placed it under the Fidelius Charm making himself the secret keeper so no one would ever find it.
Harry decided that he would meet tom riddle for the first time in Diagon ally when he went to get his school supplies and make sure that tom was ready for school this time unlike the last. It was august twenty second when Harry received his Hogwarts letter but it surprised the hell out of him was that it was addressed to Mr Harry Slytherin. Harry performed a few family tree tracing spells and he learned that his mother wasn't a mudblood but a pure blood Slytherin witch a direct descendent of Salazar himself that was adopted by the Evens family. This obviously made, Harry's task much easier for Harry as he would now have automatic respect when he was sorted into Slytherin with tom.
Harry had also snuck into the ministry of magic to read the file on himself it, said that his parents in there will before they died emancipated him and left all seven of their vaults to him. But since he was only six when it happened he was sent to live in a foster home in the muggle world since while he was legally an adult in the magical world, he was still a minor in the muggle world. He was with the smith family for a four year period where he was physically abused Intel he ran away. Seeing this harry wondered who, or what would of taken all these precautions to protect him and his false story when he received another letter from Hogwarts but not from a person the actual Hogwarts castle. It told him that since he was a descendent from the main line of Slytherin no matter his intentions the school had to protect him, and that since in this time his mother and brother were alive it canceled out the protection since they allowed the harm and encouraged it .