Let's see, I think it'd be cool if Torkoal learned Smog and Gyro ball in place of Flamethrower and Body Slam. Torkoals Heat Wave is far more powerful than its Flamethrower, and I believe Smog has previously been portrayed as being flammable, so it would work out well. Being round means that Gyro Ball would work quite well, especially if Ash wants to bring back Counter Shield.
Greninja should have Night Slash, nuff said.
Charizard gets Seismic toss back in place of Slash. Could see Iron tail replacing Dragon Tail, maybe the Flame on its tail could heat up the rest of the tail when it uses this move.
Swellow gets Steel wing instead of.... Peck.
Maybe Donphan could have High Horsepower in place of Take Down? Don't really see them being any different from one another, except that Donphan gets a move of the same type.
Incineroar gets Darkest Lariat instead of Fire Fang. I could see it working well with Ash's Counter Shield strategy.
Hawlucha gets Arial Ace or Acrobatics instead of Karate Chop, and Steel Wing replaces X-Scissor.
Lycanroc can learn Fire Fang in place of Bite to cover some of its weaknesses. Plus it would give Ash more versatility if he ever wanted Lycanroc to use Inferno overdrive.
Melmetal could learn Ice Punch maybe, and possibly Rest?
Pikachu gets Extremespeed, because why not?
Give metronome to Snorlax in place of Headbutt, because let's give him more than 6 moves! Also Z metronome could be quite useful.