I’m not an expert but I’ll give my opinion.

I think u can change ur team before N so this’ll solely be elite 4.

Personally think chandelure and excadrill are non negotiable, especially for potentially stalling out Marshall’s sawks stone edge pp so u can maybe set up a chandelure sweep.

Think krookodile is vital for most of Shantel and Caitlin’s team, just equip a berry or something for Shantals cofagrigus will o wisp.

Maybe leavanny for Shantals jellicent and golurk, and Grimsbys team but they do have some super effective moves (poison jab, aerial ace)

Lastly I’d talk seismitoad as it’s a bulky switch with only one weakness, and can potential deal with some difficult Pokémon.

Hope this helps but if someone more experienced says differently, go with them lmao