A superficial change with literally no reason for it to have happened. It's intentional and for a reason. This change in design separates OG Ash and Movie 20 Ash for a specific reason. Why change Ash's iconic hat for the movie that most think is just a retelling of the first few episodes? Doesn't make sense. They didn't do it just for the lulz
Well the truth is that it is only a cosmetic change without much importance since in the beginning of the adventure of Ash would be the one we all know, only better because we would see a little closer to Ho-Oh and would not be Misty Nor Brock, in my opinion.
No, seriously the reason why it is that they changed the design of the cap I believe that more than anything is to draw the attention of the nostalgic public saying "that the thing will be different because the cap is new" so I do not really have a Good feeling of how the movie ended up.