That should be obvious but first and foremost I'd give Ash a Chespin.
If I had the power to force only ONE thing in the show it would be that. But you all know that already, right?
Second, I'd have Ash using more red on his look. You know, I'm getting newfond appreciation for the DP outfit because that black shirt with a yellow strip finally got rid of all that blue on his look.
Granted, it seems like they've decided Ash's iconic look would red hat with a blue shirt but if you got things such as the departure of fingerless gloves (for the show at least since the AU still got them) and Ash now got shorts rather than pants, a simple color change isn't too way out the realm of possibility. Just give me more red on my Ash, darn it!
Third is a pack of mostly minor things:
- Promote Sawyer to travelling companion 'cause I got a bias. I feel like he is more fitting the role of a "smart guy" in a group than a rival for Ash. I dunno, he doesn't seem like the battler type for me. Also, change the design of his eyes a bit. I get the intention is to link him to his starter (Treecko line) but it just gives the audience the wrong first impression of the character. I mean, one look at him and people would think he is a smug, know-it-all rather than the sweet, polite and kind child he is. Just let him fully open his eyes lol
- Introduce Verity in the main show. I think her character has plenty of untapped potential even if she end up not being Cynthia's kid. I wish we could see more of what her friendship/dynamic with Ash would end up being since Yuyama said their intention was to have more of that in the movie but they cut it because of time. She's a nice compromise for DP promotion if we really can't get Dawn back. I'd probably cast Shoko Nakagawa to play her. Or I'd mess everyone's minds by casting Aoi Yuuki and directing her to do the Natsume Amano voice lol. For a more mainstream option, I'd cast Ryoko Shiraishi. Love her on Ryusoulger.
- Make an episode doing a parody/homage to Raijin-Oh and the Eldoran trilogy. Rika Matsumoto, Ikue Ohtani and Megumi Hayashibara had major roles there and it's baffling we never got any sort of homage. Biggest dissapointment was the SM schoolplay filler never doing it despite it awknowledging most of Hayashibara's major anime roles. Darn, they've done nods to Ultraman in that filler and even freaking PreCure got more than it deserved on a later one.
- Goh's Scorbunny should have had a different fate than the one it end up getting
That's all the ones I can remember for now.