... No not at all. You completely misinterpreted my message in every single way. If you cut down the tree then you're able to get said items: 1. TM 46 Thief, 2. Grass Memory, 3. A Zygarde Cell, 4. Field Notes.
After you're done getting those items you can go back to the past, interact with the area where you chopped down the cherry tree, and then you can replant it. After that when you go back to the route everything is normal again and you can give the field notes to the researcher blocking the path and then they will move and you will be able to capture a pretty powerful fairy type Pokemon.