Pokemon games have rules that limit the experience to a certain extent, like not being able to catch a wild Pokemon after it faints, not being able to withdraw from Trainer battles, or having to progress through the story as intended. For example, Pokemon Brilliant Diamond and Shining Pearl won't let players access some areas until they acquire a specific HM to use and the respective Gym Badge to unlock it. This is something that's been true since Pokemon Red and Blue, at least until Sun and Moon, and there is no changing that in the official games unless it's through glitches.
Some players feel Pokemon games are becoming too easy as time passes, and they look for a tougher challenge while playing. This is the reason why the so-called Nuzlocke Challenge was conceived, as it makes the base game harder with a new set of self-imposed rules, like only being able to catch the first wild Pokemon that appears in any given area. There are lighter and harder versions of the Nuzlocke that players might want to try out, but as it stands, any deviation from the core rule set is not officially supported in-game, and that should change.
Changing The Rules in Pokemon Games
Allowing Pokemon fans to try their own homemade rules in official games could lead to prolonged engagement with the games, as it would allow players to explore all sorts of options within their playthroughs. The only real issue would concern how players can alter the rules of their games to make it easier to get specific Pokemon, or feature unofficial variations in terms of stats and abilities or evolutions and colors. In these cases, that specific save could be banned from official tournaments and competitive battles, but two given players sharing the same rules should be able to play with one another.
Beyond that, there is no harm in allowing players to customize their playthroughs. Anyone could try and experience a Nuzlocke run with preset rules, meaning any Pokemon that faints in battle would automatically be released. Something like this could allow Pokemon fans to even get more creative with their rules, invent new challenges and truly play the way they want.
Some players might want to try a Nuzlocke Challenge but with lighter, more forgiving rules like having a single revive after each Gym is defeated. Some might prefer their playthroughs to be harder, with Trainers featuring monsters that are competitively trained and at a higher level than the base ones. It's easy to out-level all base Trainers in Pokemon Brilliant Diamond and Shining Pearl because players have access to the Grand Underground in between Gyms, and experience is shared between all Pokemon on the team.
Even turning off core features from the game could make a beneficial experience to some players if they were optional, such as the aforementioned experience share in Pokemon Brilliant Diamond and Shining Pearl. Gen 4 remakes also come with an affection and friendship system that's been common in modern games, meaning sometimes Pokemon resist knock-outs out of love for their Trainers or land more critical hits. Having the option to turn that off would be great because not everyone wants it making the experience that much easier. Overall, customization in Pokemon games has a long way to go, and allowing players to set their own rules would be a great start.
Pokemon Brilliant Diamond and Shining Pearl are available now on Nintendo Switch.